- Add custom_workouts and custom_workout_exercises tables (schema)
- New endpoints:
- GET /api/exercises - List all exercises for picker
- POST /api/custom-workouts - Fork program workout
- GET /api/custom-workouts - List user's custom workouts
- GET /api/custom-workouts/:id - Get workout with exercises
- PUT /api/custom-workouts/:id - Update workout exercises
- DELETE /api/custom-workouts/:id - Delete custom workout
- Updated endpoints for source_type support:
- GET /api/logs - Filter by source_type and custom_workout_id
- POST /api/logs - Save with source_type and custom_workout_id
- DELETE /api/logs - Support custom workout log deletion
- Adds Phase 4 planning overview
Completes: 04-01-schema-migration, 04-02-backend-api
Next: 04-03-frontend-workout-edit
