Listen on /openrouter/completions for FIM

Continue sends FIM to openrouter to /completions, let's add that route

Author: jhrozek

src/codegate/providers/openrouter/provider.py

@@ -36,6 +36,7 @@ def provider_route_name(self) -> str:
     def _setup_routes(self):
         @self.router.post(f"/{self.provider_route_name}/api/v1/chat/completions")
         @self.router.post(f"/{self.provider_route_name}/chat/completions")
+        @self.router.post(f"/{self.provider_route_name}/completions")
         @DetectClient()
         async def create_completion(
             request: Request,