refactor(gateway): restructure gateway with new dependency injection and services

Reorganize app/gateway/ with:
- common/ - lifespan management
- dependencies/ - FastAPI dependency injection (db, checkpointer, repositories, stream_bridge)
- services/runs/ - run execution services (facade_factory, input adapters, store operations)
- registrar.py - router registration
- router.py - main router setup

Simplify app.py to use the new modular structure.
Remove deprecated utils.py.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/gateway/registrar.py

@@ -0,0 +1,132 @@
+from collections.abc import AsyncGenerator
+from contextlib import asynccontextmanager
+from pathlib import Path
+from typing import Any
+
+from fastapi import FastAPI
+from fastapi.responses import HTMLResponse
+from fastapi.staticfiles import StaticFiles
+from scalar_fastapi import AgentScalarConfig, get_scalar_api_reference
+from starlette.middleware.cors import CORSMiddleware
+from store.persistence import create_persistence
+
+from app.gateway.common import lifespan_manager
+from app.gateway.router import router as gateway_router
+from app.infra.run_events import build_run_event_store
+from app.infra.storage import FeedbackStoreAdapter, RunStoreAdapter, ThreadMetaStorage, ThreadMetaStoreAdapter
+from app.plugins.auth.authorization.hooks import build_authz_hooks
+from app.plugins.auth.injection import install_route_guards, load_route_policy_registry, validate_route_policy_registry
+from app.plugins.auth.security import AuthMiddleware, CSRFMiddleware
+
+STATIC_DIR = Path(__file__).resolve().parents[1] / "static"
+STATIC_MOUNT = "/api/static"
+SCALAR_JS_URL = f"{STATIC_MOUNT}/scalar.js"
+
+
+@lifespan_manager.register
+@asynccontextmanager
+async def init_persistence(app: FastAPI) -> AsyncGenerator[dict[str, Any], None]:
+    """Initialize persistence layer (DB, checkpointer, store)."""
+    app_persistence = await create_persistence()
+
+    await app_persistence.setup()
+    run_store = RunStoreAdapter(app_persistence.session_factory)
+    thread_meta_store = ThreadMetaStoreAdapter(app_persistence.session_factory)
+    feedback_store = FeedbackStoreAdapter(app_persistence.session_factory)
+
+    try:
+        yield {
+            "persistence": app_persistence,
+            "checkpointer": app_persistence.checkpointer,
+            "store": None,
+            "session_factory": app_persistence.session_factory,
+            "run_store": run_store,
+            "run_read_repo": run_store,
+            "run_write_repo": run_store,
+            "run_delete_repo": run_store,
+            "feedback_repo": feedback_store,
+            "thread_meta_repo": thread_meta_store,
+            "thread_meta_storage": ThreadMetaStorage(thread_meta_store),
+            "run_event_store": build_run_event_store(app_persistence.session_factory),
+        }
+    finally:
+        await app_persistence.aclose()
+
+
+@lifespan_manager.register
+@asynccontextmanager
+async def init_runtime(app: FastAPI) -> AsyncGenerator[dict[str, Any], None]:
+    """Initialize StreamBridge for LangGraph-compatible runtime endpoints."""
+    from app.infra.stream_bridge import build_stream_bridge
+
+    async with build_stream_bridge() as stream_bridge:
+        yield {
+            "stream_bridge": stream_bridge,
+        }
+
+
+def register_app() -> FastAPI:
+    app = FastAPI(
+        title="DeerFlow API Gateway",
+        version="0.1.0",
+        docs_url=None,
+        redoc_url=None,
+        lifespan=lifespan_manager.build(),
+        openapi_tags=[
+            {
+                "name": "threads",
+                "description": "Endpoints for managing threads, which are conversations between a human and an assistant. A thread can have multiple runs as the conversation progresses."
+            }
+        ]
+    )
+
+    app.state.authz_hooks = build_authz_hooks()
+
+    _register_static(app)
+    _register_routes(app)
+    _register_scalar(app)
+    _register_auth_route_policies(app)
+    _register_middlewares(app)
+
+    return app
+
+
+def _register_static(app: FastAPI) -> None:
+    app.mount(STATIC_MOUNT, StaticFiles(directory=STATIC_DIR), name="static")
+
+
+def _register_routes(app: FastAPI) -> None:
+    app.include_router(gateway_router)
+
+
+def _register_auth_route_policies(app: FastAPI) -> None:
+    registry = load_route_policy_registry()
+    validate_route_policy_registry(app, registry)
+    app.state.auth_route_policy_registry = registry
+    install_route_guards(app)
+
+
+def _register_middlewares(app: FastAPI) -> None:
+    app.add_middleware(
+        CORSMiddleware,
+        allow_origins=["*"],
+        allow_credentials=True,
+        allow_methods=["*"],
+        allow_headers=["*"],
+        expose_headers=["*"],
+    )
+    app.add_middleware(CSRFMiddleware)
+    app.add_middleware(AuthMiddleware)
+
+
+def _register_scalar(app: FastAPI) -> None:
+    @app.get("/docs", include_in_schema=False)
+    def scalar_docs() -> HTMLResponse:
+        return get_scalar_api_reference(
+            openapi_url=app.openapi_url,
+            title=app.title,
+            scalar_js_url=SCALAR_JS_URL,
+            agent=AgentScalarConfig(disabled=True),
+            hide_client_button=True,
+            overrides={"mcp": {"disabled": True}},
+        )