feat: add data backup/import, goal step ordering, and PostgreSQL migration

- Add GET /api/backup/export and POST /api/backup/import endpoints for full data backup
- Add drag-and-drop reorder for goal steps with PUT /api/goals/{id}/steps/reorder
- Auto-assign sort_order on step creation (preserves creation order)
- Fix duplicate milestone rendering in goal detail page
- Add category management button in goal dialog
- Migrate database default from SQLite to PostgreSQL
- Fix router guard redirect loop for logged-in users on setup/login pages
- Fix ALTER TABLE ADD COLUMN crash on callable defaults (uuid.uuid4)
- Add auth status rate limiter and token version caching
- Update CLAUDE.md to reflect current architecture

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

requirements.txt

@@ -5,5 +5,5 @@ pydantic==2.5.3
 pydantic-settings==2.1.0
 python-multipart==0.0.6
 python-jose[cryptography]==3.3.0
-passlib[bcrypt]==1.7.4
 bcrypt==4.0.1
+psycopg2-binary==2.9.11