fix: remove empty-path GET decorator to avoid FastAPI prefix+path empty error

When dashboard router is mounted with prefix="" the @router.get("") route
causes FastAPIError: Prefix and path cannot be both empty.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/routes/dashboard.py

@@ -15,7 +15,6 @@ from dashboard_cache import get_cached, is_warm
 router = APIRouter()
 
 
-@router.get("")
 @router.get("/")
 async def dashboard_page(request: Request):
     config = request.app.state.config