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/02 - Features/Auth.md

@@ -0,0 +1,28 @@
+# Feature: Auth
+
+**Module path:** `lib/features/auth/` + `lib/core/auth/`
+
+## Overview
+Handles user login, registration, and session management.
+
+## Screens
+- `login_screen.dart` — Mobile login
+- `desktop_login_screen.dart` — Desktop login
+
+## Key Files
+| File | Purpose |
+|------|---------|
+| `lib/core/auth/` | Auth logic, tokens, session |
+| `lib/features/auth/` | Auth feature UI & state |
+
+## Flow
+- [ ] Document login flow
+- [ ] Document registration flow
+- [ ] Document session persistence (shared_preferences?)
+
+## Notes
+> Add notes about OAuth, JWT, or custom auth as you discover them
+
+## Related
+- [[01 - Architecture/State Management]]
+- [[04 - API & Backend/API Notes]]