feat(ai): python graphql federation subgraph with strawberry

- strawberry-graphql[asgi] dependency added

- GeneratedReport and LessonPlanStatus @key types with resolve_reference

- RouterAuthMiddleware validates Router-Authorization header on /graphql

- GraphQL endpoint mounted at /graphql in FastAPI app

- WorkflowStateStore injected for lesson plan status resolution

services/ai/pyproject.toml

@@ -20,6 +20,8 @@ dependencies = [
     "redis>=5.1.0",
     # 重试机制（LLM 调用 + 下游 gRPC）
     "tenacity>=9.0.0",
+    # GraphQL Federation 2 子图（v2.1 M1，Apollo Router 组合）
+    "strawberry-graphql[asgi]>=0.257.0",
 ]
 
 [tool.uv.sources]