feat: brain service — self-contained second brain knowledge manager

Full backend service with:
- FastAPI REST API with CRUD, search, reprocess endpoints
- PostgreSQL + pgvector for items and semantic search
- Redis + RQ for background job processing
- Meilisearch for fast keyword/filter search
- Browserless/Chrome for JS rendering and screenshots
- OpenAI structured output for AI classification
- Local file storage with S3-ready abstraction
- Gateway auth via X-Gateway-User-Id header
- Own docker-compose stack (6 containers)

Classification: fixed folders (Home/Family/Work/Travel/Knowledge/Faith/Projects)
and fixed tags (28 predefined). AI assigns exactly 1 folder, 2-3 tags, title,
summary, and confidence score per item.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

services/brain/app/main.py

@@ -0,0 +1,41 @@
+"""Brain service — FastAPI entrypoint."""
+
+import logging
+
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+from app.api.routes import router
+from app.config import DEBUG
+
+logging.basicConfig(
+    level=logging.DEBUG if DEBUG else logging.INFO,
+    format="%(asctime)s %(levelname)s %(name)s: %(message)s",
+)
+
+app = FastAPI(
+    title="Second Brain",
+    description="Save everything. AI classifies it. Search it later.",
+    version="1.0.0",
+    docs_url="/api/docs" if DEBUG else None,
+    redoc_url=None,
+)
+
+# No CORS — internal service only, accessed via gateway
+app.include_router(router)
+
+
+@app.on_event("startup")
+async def startup():
+    from app.database import engine, Base
+    from app.models.item import Item, ItemAsset, AppLink  # noqa: import to register models
+
+    # Create tables if they don't exist
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+
+    # Ensure Meilisearch index exists
+    from app.search.engine import ensure_meili_index
+    await ensure_meili_index()
+
+    logging.getLogger(__name__).info("Brain service started")