add service management commands and restructure CLI #52

Service management integrated as top-level verbs: enable, disable,
start, stop, restart, reload, status, logs. Backed by s6rc module
(src/s6rc.zig) that delegates to s6-rc repo commands.
mere status with no args lists all services; with a name shows
detail view with graceful degradation when not running as root.
Restructure CLI help into grouped sections with intentional ordering:
- Package Management: search, install, uninstall, shell, profile,
 etc, store, dev
- Service Management: enable, disable, start, stop, restart, reload,
 status, logs
Move key under dev. Move gc (renamed to clean), verify, pin,
generation, and init under mere store.
Consolidate docs: trim service-management.md, fold namespaces.md
into spec, update CLI references across all design docs and README.

Defaults to true (auto-generate logging pipeline). Set to false for
services that feed another logger (e.g., klogd -> syslogd).
Parsed from recipe KDL as a simple bool child node: log false