chore: remove vibe-coding artifacts from tracking, sync notes and obsidian config

- Untrack .claude/launch.json (Claude Code config)
- Add .claude/, .mcp.json, CLAUDE.md, and AI-generated CSVs to .gitignore
- Add _notes/ vault (architecture, API, tasks, bugs, infra docs)
- Add .obsidian/ plugin/vault config (workspace state excluded)
- Sync CHANGELOG.md

_notes/01 - Architecture/State Management.md

@@ -0,0 +1,22 @@
+# State Management
+
+## Approach
+Eventify uses **Provider** (`^6.1.2`) for state management.
+
+## Pattern
+- `ChangeNotifier` classes hold state
+- `ChangeNotifierProvider` exposes state to the widget tree
+- `Consumer<T>` / `context.watch<T>()` rebuilds UI on state change
+- `context.read<T>()` for one-off reads without subscribing
+
+## Key Providers
+> Fill in as you identify providers in `lib/core/` and `lib/features/`
+
+| Provider | Location | Responsibility |
+|----------|----------|----------------|
+| AuthProvider | `lib/core/auth/` | Session, login/logout |
+| ThemeManager | `lib/core/theme_manager.dart` | Dark/Light mode toggle |
+
+## Notes
+- Desktop and mobile screens share the same providers via `responsive_layout.dart`
+- Local persistence uses `shared_preferences` (not Provider)