feat: frontend modernization with HTMX, Alpine.js and Plyr (Phase 3)

- Integrated HTMX for server-driven UI updates and fragments
- Adopted Alpine.js for global reactive state and tab management
- Replaced legacy player with Plyr.io for premium streaming experience
- Implemented real-time download polling via HTMX
- Added server-sent Toast notification system
- Fixed navigation and authentication scoping issues

main.py

@@ -133,7 +133,6 @@ from app.routers import (
 app.include_router(root_router)
 app.include_router(auth_router)
 app.include_router(downloads_router)
-app.include_router(downloads_legacy_router)
 app.include_router(anime_router)
 app.include_router(favorites_router)
 app.include_router(recommendations_router)