v0.6.0: major UX/reliability release

Watch (app/index.js):
- Screen always on for the session; dims after 20s idle, never sleeps;
  any tap restores brightness (display.autoOff=false + brightnessOverride)
- Sync safety: pendingWorkout persisted through syncing/sync_error; a
  finished-but-unsynced workout survives app death and offers RETRY
- Flat set-sequence engine: supersets (superset_id) interleave round-robin
  with rest only after each round; skip-exercise removes remaining entries
  and persists across restarts
- Weight carry-forward as per-exercise DELTA (preserves pyramids; warmups
  excluded both ways)
- UNDO last set via top-right circle during rest; BACK on confirm-finish
  un-logs the last set (fixes double-log bug)
- Hold +/- auto-repeats every 200ms; weight step accelerates 0.5 -> 2.5 kg
- Rest: 5s pre-warning ping, nudge-max at 0:00, then counts overrun up
  (+m:ss, orange) until GO; planned vs actual rest logged per rest
- Rest timer resumes after restart (deadline-based)
- HR stats per set + session (avg/max); summary written to Hevy workout
  description together with rest stats
- 'prev' line: last logged sets per exercise; NEXT-exercise highlight
  (teal title) during rest when the upcoming set is a new exercise
- Color-coded adjust modes (REP yellow / KG teal / RPE orange)
- Set-type badges: WARMUP / DROP / FAIL on the set counter
- Plate calculator overlay (20 kg bar, per-side breakdown) on tapping the
  weight line of barbell exercises
- Routine picker: LIST on idle -> browse routines with </> -> GO
- PLAN_NACK: requests resend of lost plan pages (3 attempts)
- SET_LOG: every completed set mirrored to the companion as backup

Companion (companion/index.js):
- prev-performance map from last 10 workouts attached to plans
- superset_id passthrough; workout description passthrough
- GET_ROUTINES / SYNC_ROUTINE for the watch routine picker
- WORKOUT_NACK: requests resend of lost workout pages (3 attempts)
- Per-set backup in localStorage/settingsStorage, cleared on SYNC_OK

Resources: prev-info text element, tap-weight tap zone