report pausedSteam and puffing as themselves, not as idle - #800

Summary

mapDe1SubToMachineSubstate collapsed five raw DE1 substates onto MachineSubstate.idle. Two of
them are steam phases a caller has a real reason to tell apart:

pausedSteam (0x12) the valve is shut and the session is not over
puffing (0x14) the purge after steam stops on time or on milk temperature

Reported as idle, neither could be shown, and a client could not distinguish a pause from a purge
from a machine doing nothing at all. The purge matters most: it can hold for a while, and a
screen that cannot name it leaves someone watching a machine that looks stopped and is not.

noState, userNotPresent and refill still map to idle — they carry no phase a caller can act
on.

Base: main. Independent. Two files, 15 lines.

What this could have broken, and does not

shot_sequencer ends a shot when the substate reads pouringDone or idle, so a steam session
arriving as idle used to satisfy it. It never reaches that branch: the sequencer leaves idle
only on espresso + preparingForShot, and aborts in preheating if the state is not espresso,
so steam never enters ShotState.pouring. Every other reader compares against a specific substate
rather than switching exhaustively.

Linked Issue

N/A

Verification

• flutter analyze — clean.

• flutter test — full suite 3891 passed against current main.

• dart format — clean on every changed file.

• The sequencer reasoning above was checked against the code, not assumed.

• Verified on hardware. This change ships in the Decaid-Canary build Ben runs on his own
  machine, and has been exercised in normal use rather than only under test.

Impact

• API: MachineSubstate gains two values that were previously reported as idle. A client
  switching exhaustively on the enum must handle them.
• Compatibility: a client comparing against specific substates is unaffected. One that treats
  "not a substate I know" as idle keeps today's behaviour.
• User-visible: a skin can now name the steam pause and the purge.
• Security: none.

Contributor Responsibility

AI-assisted development is allowed. The submitter remains responsible for the submitted work.

• I have reviewed and understand all changes in this PR and take responsibility for their correctness, security, behavior, licensing, and provenance, including any AI-assisted or AI-generated work.