fix: read merged runtime config in containerized mode

The FastAPI app now checks for /tmp/runtime_config.json (created by
entrypoint.sh config merger) before falling back to the default config.

This allows user-provided configs mounted at /app/user-configs/ to
properly override default values in containerized deployments.

Fixes issue where custom user configs were not being applied.

api/main.py

@@ -116,7 +116,7 @@ class HealthResponse(BaseModel):
 
 def create_app(
     db_path: str = "data/jobs.db",
-    config_path: str = "configs/default_config.json"
+    config_path: str = "/tmp/runtime_config.json" if Path("/tmp/runtime_config.json").exists() else "configs/default_config.json"
 ) -> FastAPI:
     """
     Create FastAPI application instance.