Add glossary, ADRs and future ideas from design grilling

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/adr/0001-v1-foundations.md

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+# ADR 0001 — v1 foundations
+
+Status: Accepted (2026-10-28)
+
+## Decisions
+
+1. **Platform**: Flutter, Android only.
+2. **Modes**: A global Stretching / Workout switch that changes design, content and everything else.
+3. **Content**: A large bundled Exercise Library; users create all Plans themselves (no built-in Plans).
+4. **Data**: Offline only, local on-device storage, no accounts.
+5. **Sessions**: Guided Player (timers, rest countdown, cues) rather than a checklist.
+6. **History**: Simple log (date, Plan, duration) + Streak.
+7. **Visuals**: Simple animations are desired, but may be deferred past v1.
+8. **Scheduling / reminders**: Not in v1.
+
+## Consequences
+
+- No backend; all persistence is a local database on the device.
+- The Exercise Library must be bundled in the APK, so its size (incl. images) matters.

docs/adr/0002-library-ui-and-player.md

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+# ADR 0002 — Exercise library, mode design, Player cues
+
+Status: Accepted (2026-10-28)
+
+## Decisions
+
+1. **Library source**: free-exercise-db (Unlicense, 876 exercises). `stretching` → Stretching mode,
+   everything else → Workout mode. No user-created exercises.
+2. **Images**: Bundle both images per exercise, compressed to WebP (~400px, est. 15–20 MB).
+   The start/end "flip" is the v1 animation; real animations are a future step.
+3. **Language**: English only; UI strings centralised for later translation.
+4. **Plan Steps**: Workout = sets, reps-or-duration, optional weight; no rest countdown.
+   Stretching = hold, both-sides flag, rounds. Workout Steps can be grouped into Supersets.
+5. **Library browsing**: search + muscle/equipment/level filters, reused as the Plan exercise picker.
+6. **Structure & design**: Mode switch at top; per-mode tabs Plans · Library · History.
+   Stretching = calm/light (sage/teal, rounded, slow). Workout = dark/energetic (orange/red, bold, snappy).
+   Last-used mode is remembered.
+7. **Player cues**: Visual cues (countdown ring, accent pulse, next cards, auto-advance, screen kept on)
+   plus a gentle, non-annoying sound. No vibration.
+8. **History**: Separate per Mode. The Streak is one shared, Duolingo-style daily Streak across both Modes;
+   only complete Sessions count.
+9. **Units**: kg only.

docs/adr/0003-tech-stack-follows-cookit.md

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+# ADR 0003 — Tech stack follows CookIT
+
+Status: Accepted (2026-10-28)
+
+ZenXercise uses the same stack and conventions as the author's CookIT app (local-first Flutter, Android),
+so both codebases read alike.
+
+- State: `provider` with `ChangeNotifier` controllers, wired in `main.dart` via `MultiProvider`.
+- Persistence: `drift` + `drift_flutter` (SQLite); `shared_preferences` for small settings (last Mode).
+- Navigation: plain `Navigator` with named routes (no go_router).
+- Strings: `flutter gen-l10n` with ARB files in `lib/src/localization` (`app_en.arb` template).
+- Layout: `lib/src/<feature>/` with repositories, controllers and `views/`.
+- Screen-on in the Player: `wakelock_plus`. IDs: `uuid`.
+- Tests: `flutter_test`, `mocktail`, `sqlite3` (in-memory drift in tests).
+- Lints: `flutter_lints`. Docs: `GLOSSARY.md` (term / definition / _Avoid_) and `docs/adr/`.
+
+Supersedes the Riverpod / go_router proposal from the grilling session.