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

app/routers/__init__.py

@@ -3,10 +3,7 @@ Routers package for Ohm Stream Downloader API.
 """
 
 from app.routers.router_auth import router as auth_router
-from app.routers.router_downloads import (
-    router as downloads_router,
-    legacy_router as downloads_legacy_router,
-)
+from app.routers.router_downloads import router as downloads_router
 from app.routers.router_anime import router as anime_router
 from app.routers.router_favorites import router as favorites_router
 from app.routers.router_recommendations import router as recommendations_router
@@ -19,7 +16,6 @@ from app.routers.router_root import router as root_router
 __all__ = [
     "auth_router",
     "downloads_router",
-    "downloads_legacy_router",
     "anime_router",
     "favorites_router",
     "recommendations_router",