docs: add .planning/ project-tracking documents

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.planning/REQUIREMENTS.md

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+# Calendula — Requirements
+
+See full design spec: `docs/superpowers/specs/2026-06-08-calendar-app-design.md`
+
+## V1 Scope (Variant "B")
+
+### Validated (shipped)
+- (none yet — first milestone in progress)
+
+### Active (V1)
+
+- [ ] Foundation & CI infrastructure
+- [ ] Data Layer over `CalendarContract`
+- [ ] Permission flow (`READ_CALENDAR`)
+- [ ] Month view (S1)
+- [ ] Week view (S2)
+- [ ] Day view (S3)
+- [ ] Event Detail Sheet (S4)
+- [ ] Multi-Calendar Filter (M3)
+- [ ] Today button + Jump-to-Date (M2)
+- [ ] View-Switcher (M1)
+- [ ] Settings screen (M4)
+- [ ] Empty / no-permission / no-calendars states
+- [ ] German + English localization
+- [ ] Loading/Failure/Success states per screen (architectural pattern)
+
+### Out of Scope (V2+)
+
+- Event create / edit / delete (V2)
+- Home-screen widget
+- Full-text search
+- Quick-add
+- Custom notifications/reminders (system already handles these)
+- Tablet/foldable-specific layouts
+- iOS support (Android-only by design)
+
+## Constraints
+
+- **Tech stack:** Kotlin + Jetpack Compose + Material 3 Expressive, Hilt, DataStore
+- **Platform:** Android 10+ (API 29 minimum), Android 16 (API 36) target
+- **Offline-first:** all data lives in `CalendarContract`; no app-side network
+- **Privacy:** zero telemetry, no analytics
+- **i18n:** German + English from day one
+- **Tests + CI from day one**
+- **License:** MIT