Completed workouts can bypass Health export (endWorkout, stale-session reconcile, workout-only imports)

[abdulsaheel]

Found by CodeRabbit during #262 review (flagged as outside that PR's diff — filing separately so it isn't lost). Not a regression from #262; pre-existing behavior.

The gap

Three paths mark a session row done without ever reaching the Health store:

1. LocalRepositoryImpl.endWorkout — writes status: 'done' but never calls HealthExporter.exportWorkoutId / exportWorkout. Health export only picks sessions up inside exportAll's per-day_result scan.
2. Stale-session reconciliation (AppState._reconcileOrphanedLiveWorkout) — silently finalizes stale live rows (deliberately: no resurfacing a days-old banner), but those rows carry end_ts: null, so even if export scanned them there is no end time to export. They are permanently un-exportable as things stand.
3. Workout-only imports — an import that brings sessions but no/unchanged day_result rows can bypass exportAll's day scan entirely, so imported completed sessions never export.

Why it matters

AGENTS.md §4.7's exact failure class: capability wired into one call path but not all N. A user who finishes a workout offline (app killed mid-session → reconciled on next launch) or imports history gets silent gaps in Apple Health / Health Connect while the app shows the session as saved.

Suggested shape

• endWorkout and reconciliation set a real end_ts (reconciliation may need to derive one — e.g. last sample ts or reconcile time, stated honestly) and then route through the existing HealthExporter.exportWorkoutId(...) after the DB write lands.
• Workout-only import completion triggers an explicit session export pass (reuse existing exporter APIs; skip incomplete rows).
• Keep the current single-flight/backoff machinery — this is about adding the missing call sites, not new plumbing.

Verification ideas

• Test: end a workout with health configured → assert one export call with correct start/end.
• Test: reconcile a stale live row → exported once, not re-exported on later passes.