Add glossary, ADRs and future ideas from design grilling

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

future_ideas.md

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+# Future ideas
+
+Things deliberately left out of v1.
+
+- Real exercise animations or video (v1 uses the start/end Flip Animation)
+- iOS build (and web/desktop)
+- Accounts and cloud sync / backup
+- Scheduling Plans on weekdays, with reminder notifications
+- Built-in starter Plans
+- Custom user-created Exercises
+- Progress charts and personal records from Set Logs
+- lb units (v1 is kg only)
+- Vibration cues and voice guidance in the Player
+- Translations (v1 is English only)
+- Mixed Plans that combine Stretching and Workout (e.g. warm-up, workout, cool-down)