Composing now auto-saves a draft when you leave with anything entered, and sending
deletes it.
- New `drafts` Room table (entity + DAO + Draft model + MIGRATION_5_6, DB v6), with
repository observe/get/save/delete.
- ComposeViewModel loads a draft by id (resume), saves/updates one on exit (or deletes
it when emptied), and deletes it after sending; the screen closes via a finished event
so the save completes before navigating away.
- New Drafts screen (list with per-row delete, resume on tap); the inbox shows a
"Drafts (N)" entry when any exist. Compose gains a draft nav arg.
- assemble/test/lint green; verified on the Android 17 emulator — the v5->v6 migration
kept existing mail, a backed-out compose saved a draft, the draft listed and reopened
pre-filled, and sending it removed the draft.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
JMR-devandClaude Opus 4.8
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