Add admin panel, WebSocket support, and API versioning

Introduce an admin portal (React + Nginx), WebSocket routing, and
API versioning middleware with `/api/v1/` prefix deprecation.
Add master API key authentication, new Prometheus metrics for AI
token consumption and active WebSockets, and extend S3 config
with a public endpoint URL. Update test paths and fixtures to
align with the new routing structure.

app/routers/__init__.py

@@ -2,5 +2,7 @@ from app.routers.images import router as images_router
 from app.routers.ai import router as ai_router
 from app.routers.auth import router as auth_router
 from app.routers.files import router as files_router
+from app.routers.websocket import router as ws_router
+from app.routers.admin import router as admin_router
 
-__all__ = ["images_router", "ai_router", "auth_router", "files_router"]
+__all__ = ["images_router", "ai_router", "auth_router", "files_router", "ws_router", "admin_router"]