feat: Skills & Methods catalog complete
Backend:
- Created routers/skills.py with full CRUD
- Skills: list (with category filter), get, create, update, delete
- Methods: list (with category filter), get, create, update, delete
- Default: only show active items
- Read access: all authenticated users
- Write access: admin only
- Registered skills router in main.py
Frontend:
- Complete SkillsPage with 2 tabs (Fähigkeiten, Trainingsmethoden)
- Browse by category with cards layout
- Admin CRUD forms (importance rating for skills, duration/group size for methods)
- Mobile-responsive grid layout
- Updated api.js with all skill/method functions
- Added /skills route to App.jsx
Migration already exists: 003_catalogs.sql (skills, training_methods + seed data)
Next: Training Planning (core feature)