feat: add "comic" source type for daily comic strips (XKCD, gocomics.com, arcamax.com) - #133

Downloads today's XKCD, Calvin and Hobbes, or Garfield strip and embeds it
as a single image Story. The fetch mechanism - page URL, per-comic request
headers, and the XPath used to locate the strip's <img> tag - is ported
from evidlo/remarkable_news's systemd service definitions (services/
xkcd.service, cah.service, garfield.service), which use the same approach
to push comics onto a reMarkable's suspend screen.
The downloaded strip is inlined as a base64 data: URI rather than linked
by remote URL: gocomics.com requires the same browser-like headers for the
image request as for the page request, and WeasyPrint (which fetches
<img src> URLs itself while rendering the PDF) has no way to attach them.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Embedding the raw fetched bytes directly as a base64 data: URI seemed fine
in isolation, but broke silently on the real Garfield source: arcamax.com
serves a CMYK JPEG with a large embedded Photoshop/ICC metadata block, and
passing that straight to WeasyPrint made it drop the *entire* story with no
exception and no log line - just an empty gap where "Comics" should have
been, confirmed only by diffing rendered PDF text against the source HTML.
Decode with Pillow and re-encode as a clean PNG before embedding, converting
to RGB/L first when the source isn't already one of those modes (handles
CMYK and any other decode-only mode a comic site might serve). This mirrors
remarkable_news's own Go tool, which never embeds fetched bytes directly
either - it decodes then re-encodes via imaging.Decode/imaging.Save.
Pillow was already a transitive dependency via weasyprint; now declared
directly since comic.py imports it.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

The Pillow re-encode from the previous commit fixed the CMYK/metadata
case but not the general one: gocomics.com's CDN can serve a strip at
2800px+ wide with no smaller variant requested, and even at a source's
default resolution, a lossless PNG re-encode of a dithered/gradient-heavy
color strip is several times larger than the same content as JPEG. Either
way the resulting base64 payload (multi-hundred-KB, sometimes >1MB for a
single story) combined with the hundreds of other images already in a full
newspaper was enough to make WeasyPrint silently drop the story entirely -
confirmed by bisecting a real "Julians Zeitung" generation down to the
image size specifically, after ruling out layout, section ordering, and
provider wrapping as causes.
Cap the long edge to _MAX_IMAGE_DIMENSION (1200px) and switch the
re-encode target from PNG to JPEG (quality=90) - matching remarkable_news's
own Go tool, which resizes to the target screen size and always saves via
imaging.JPEGQuality, never PNG. Verified against all three live sources:
body_html size dropped from >1MB to ~300KB (Calvin and Hobbes) and
~125KB (Garfield).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Previously: XKCD's headline was the strip's own per-day title (from its <img>
alt text), while Garfield/Calvin and Hobbes fell back to "<name> - <date>" -
and every comic additionally set byline=<name>. Two problems in practice:
- XKCD showed headline "Main Span" with byline "XKCD" right underneath it -
 looks like a subheading, but for a single-panel strip there's no
 "subheading" to show, just the same source name the reader already knows
 from the section it's in.
- Garfield/CaH's "<name> - <date>" headline duplicated the name that was
 *also* set as the byline right below it - e.g. headline "Garfield -
 August 02, 2026" directly above byline "Garfield" is the same identifier
 twice in a two-line block, worse when two comics share one "Comics"
 section and both do this right next to each other.
Now every comic gets a single, fixed headline - "XKCD", "Garfield", or
"Calvin and Hobbes" - and no byline. Unlike an RSS article, where the byline
distinguishes otherwise-anonymous entries pulled from different feeds into
one section, a comic's headline already *is* that identifier - a byline
under it, or a per-day headline that just restates it, adds nothing.
XKCD's own per-day title/mouseover joke aren't lost: the title still ends
up in the embedded <img>'s alt attribute, and the joke still renders as a
caption underneath, exactly as before - only the *headline* source changed.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Pillow's Image.convert("RGB") does not composite transparent pixels against
anything - it just drops the alpha channel and keeps whatever RGB value (or,
for a GIF's transparency-color-key, whatever palette color) was stored
underneath. Verified directly against Pillow: a semi-transparent black RGBA
pixel converts to solid black, not white; a color-keyed "transparent" GIF
pixel converts to its own arbitrary palette color. Applied unconditionally,
this could leave visible phantom colors/edges wherever a source image used
transparency - not observed against any of the three real sources today (all
consistently serve opaque images), but a real gap for a hypothetical source
that does.
Composite onto white before dropping alpha whenever the source image has any
transparency (RGBA/LA/PA mode, or a GIF-style transparency color-key) - white
because a comic strip always sits on a plain newspaper page, and every
bundled goosepaper style renders that page white.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

pyproject.toml has declared pillow directly (see the earlier "comic" source
type commit) but uv.lock's own per-package listing for goosepaper never
picked it up as a direct dependency - only the transitive entry already
present via weasyprint existed. Regenerated via `uv sync`.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Replaced the two site-specific, hardcoded comic_type entries ("cah" for
Calvin and Hobbes, "garfield") with two generic site-backed ones:
comic_type "gocomics"/"arcamax" plus a required comic_name (the comic's
own slug on that site, e.g. "garfield" or "beetlebailey"). Both sites
serve every comic in their catalog through one identical URL/markup
template - only the slug differs - so this was verified live against
several strips on each site rather than assumed.
The one wrinkle this raises - a fixed per-comic headline no longer works
once one _ComicSource entry covers hundreds of comics - is solved by
deriving the label straight from the fetched page itself: gocomics.com's
schema.org JSON-LD ComicSeries name, arcamax.com's og:title meta tag.
No hardcoded label table to maintain as comics get added.
Also folds in a since-diagnosed reliability fix for the date-scoped
gocomics.com URL: generation running earlier in the day than the site's
(undocumented) daily rollover was failing outright every time. Rather
than guess the rollover's timezone (an earlier version of this commit
assumed US-Eastern - wrong, and unverifiable either way), it now retries
up to a few days back on a miss and logs when that happens, instead of
dropping the section. This now benefits every gocomics comic, not just
Calvin and Hobbes.
xkcd is unchanged - it only ever serves one comic.
🤖 Generated with Claude Code

Follows the same per-provider reference doc convention master now uses
for every other built-in source (see docs: add story provider guides,
upstream a556ff9) instead of the inline "## comic source options"
README section this branch carried before rebasing onto that change.

Addresses j6k4m8's review comment on this PR: type comic_type as
Literal["xkcd", "cah", "garfield"] so editors can hint/autocomplete it.
Same idea, updated to the current three values (xkcd/gocomics/arcamax)
after the generic-by-slug redesign. Kept as a manually-declared alias
next to _COMIC_SOURCES rather than derived from its keys - Literal
can't be built from a dict at type-check time (his other suggestion,
which he'd flagged as untested).
The runtime membership check in __init__ stays: Literal only helps
callers written directly in Python, not config-driven ones (see
util.py) that pass a plain str straight from JSON.

Replaces comic.py's own inline Pillow re-encode block (bound
dimensions, normalize color mode, composite transparency, always
JPEG) with a call to the new shared storyprovider/imageutil.py -
identical logic, now factored out since RSS-sourced article images
need the exact same defensive treatment for the exact same reason
(fix/rss-image-embedding, not yet upstreamed).
Both PRs carry their own copy of imageutil.py so either can merge
first without depending on the other - at worst a trivial identical-
content conflict for whichever merges second, same category of
expected mechanical overlap already called out for this PR's
config.py/util.py registry changes.
No behavior change: same tests (comic image processing already had
dedicated CMYK/transparency/oversized-image regression tests, now
also exercised directly against imageutil in test_imageutil.py),
verified live against arcamax.com/gocomics.com.
🤖 Generated with Claude Code

Same issue the maintainer flagged in j6k4m8#141 for rss.py - an unverifiable
anecdotal claim in a docstring rather than documentation.

Every DailyComicStoryProvider story already got a fixed, source-derived
headline (the comic's name, e.g. "Garfield") - kept for the table of
contents, anchor-id slugging, and dedup, but rendered as a real, always-
visible <h1 class="story-headline"> above the strip too. That's a plain
duplicate: the strip already shows its own name inside the image, so
repeating it as running text above adds nothing - unlike a headline/byline
on an RSS article, which names something the fetched content doesn't
already show on its own.
Adds Story.headline_visible (default True, no behavior change for every
other story type) - to_html() only emits the <h1>/<h2>/... tag when it's
true; the headline text itself is untouched either way, so everything
else that reads it directly still works exactly as before (table-of-
contents entries, anchor ids, deduplicate=True's headline-based
matching). DailyComicStoryProvider now always constructs its Story with
headline_visible=False - a fixed property of every comic, not a config-
exposed option, per the class docstring's now-updated rationale.
Verified live end to end against a real XKCD fetch: table of contents
still lists "XKCD" and links to the strip; the strip's own page shows
only the image and its mouseover-joke caption, no headline above it.
Full suite: 147 passed (143 previously + 4 new: goosepaper/test_story.py,
covering the new default/override/anchor-id-still-works behavior
directly, plus 2 existing comic tests (xkcd, gocomics) now also assert
headline_visible is False on the returned Story).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>