Replace non-existent emit_progress calls with proper ProgressService methods:
- start_progress for starting operations
- update_progress for progress updates
- complete_progress for successful completion
- fail_progress for failures
Convert percentage-based updates to current/total based on ProgressService API
- Create loading.html template with WebSocket-based progress updates
- Update initialization_service to emit progress events via ProgressService
- Modify setup endpoint to run initialization in background and redirect to loading page
- Add /loading route in page_controller
- Show real-time progress for series sync, NFO scan, and media scan steps
- Display completion message with button to continue to app
- Handle errors with visual feedback
- Create initialization_service.py with shared initialization functions
- Extract setup logic from lifespan and setup endpoint into reusable functions
- Setup endpoint now calls perform_initial_setup() directly
- Lifespan startup calls the same shared functions
- Eliminates code duplication between setup and lifespan
- Ensures consistent initialization behavior regardless of entry point
