refactor: migrate main.py to modular routers and add project roadmap

- Migrated monolithic main.py to feature-scoped routers in app/routers/
- Added GEMINI.md for project context and AI instructional guidelines
- Updated README.md with a comprehensive modernization plan (SQL migration, robust scraping DSL, frontend modernization)
- Improved authentication with cookie support and modular JS
- Updated test suite and documentation

app/routers/__init__.py

@@ -0,0 +1,31 @@
+"""
+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_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
+from app.routers.router_watchlist import router as watchlist_router
+from app.routers.router_sonarr import router as sonarr_router
+from app.routers.router_player import router as player_router
+from app.routers.router_static import router as static_router
+from app.routers.router_root import router as root_router
+
+__all__ = [
+    "auth_router",
+    "downloads_router",
+    "downloads_legacy_router",
+    "anime_router",
+    "favorites_router",
+    "recommendations_router",
+    "watchlist_router",
+    "sonarr_router",
+    "player_router",
+    "static_router",
+    "root_router",
+]