feat(infra): add new infrastructure layer for storage and streaming

Add app/infra/ package with:
- storage/ - repository adapters for runs, run_events, thread_meta
- run_events/ - JSONL-based event store with factory
- stream_bridge/ - memory and redis adapters for SSE streaming

This layer provides the persistence abstractions used by the gateway
services, replacing the old deerflow/persistence modules.

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

backend/app/infra/run_events/factory.py

@@ -0,0 +1,25 @@
+"""Factory for app-owned run event store backends."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker
+
+from app.infra.storage import AppRunEventStore
+from deerflow.config import get_app_config
+
+from .jsonl_store import JsonlRunEventStore
+
+
+def build_run_event_store(session_factory: async_sessionmaker[AsyncSession]) -> AppRunEventStore | JsonlRunEventStore:
+    """Build the run event store selected by app configuration."""
+
+    config = get_app_config().run_events
+    if config.backend == "db":
+        return AppRunEventStore(session_factory)
+    if config.backend == "jsonl":
+        return JsonlRunEventStore(
+            base_dir=Path(config.jsonl_base_dir),
+        )
+    raise ValueError(f"Unsupported run event backend: {config.backend}")