feat: complete calendar redesign with week-based selection and database-backed queries
Frontend changes:
- Redesigned day cells to show release titles with colored dot indicators (blue for movies, purple for TV)
- Implemented week-based selection with dimming effect (non-selected days at 40% opacity)
- Added 'Go to today' link below month header for quick navigation
- Sidebar now displays all releases for selected week sorted by date
- Removed week/month/list view toggle in favor of unified month view
- Added placeholder cells at end of calendar grid to complete final week
- Fetches 3 months of data with React Query placeholderData for smooth transitions
- Fixed React key collisions by including season/episode numbers
Backend changes:
- Release calendar API now accepts startDate and endDate query parameters
- Service layer queries database directly for episodes and watchlist items
- Eliminated per-show TMDB API calls - single database query for date range
- Updated DTOs, controller, service, and all related tests