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/docker-compose.yml

@@ -0,0 +1,104 @@
+services:
+  # ── API ──
+  brain-api:
+    build:
+      context: .
+      dockerfile: Dockerfile.api
+    container_name: brain-api
+    restart: unless-stopped
+    volumes:
+      - ./storage:/app/storage
+    environment:
+      - DATABASE_URL=postgresql+asyncpg://brain:brain@brain-db:5432/brain
+      - REDIS_URL=redis://brain-redis:6379/0
+      - MEILI_URL=http://brain-meili:7700
+      - MEILI_MASTER_KEY=${MEILI_MASTER_KEY:-brain-meili-key}
+      - BROWSERLESS_URL=http://brain-browserless:3000
+      - OPENAI_API_KEY=${OPENAI_API_KEY}
+      - OPENAI_MODEL=${OPENAI_MODEL:-gpt-4o-mini}
+      - PORT=8200
+      - DEBUG=${DEBUG:-0}
+      - TZ=${TZ:-America/Chicago}
+    depends_on:
+      brain-db:
+        condition: service_healthy
+      brain-redis:
+        condition: service_started
+      brain-meili:
+        condition: service_started
+    networks:
+      - default
+      - pangolin
+
+  # ── Worker ──
+  brain-worker:
+    build:
+      context: .
+      dockerfile: Dockerfile.worker
+    container_name: brain-worker
+    restart: unless-stopped
+    volumes:
+      - ./storage:/app/storage
+    environment:
+      - DATABASE_URL=postgresql+asyncpg://brain:brain@brain-db:5432/brain
+      - REDIS_URL=redis://brain-redis:6379/0
+      - MEILI_URL=http://brain-meili:7700
+      - MEILI_MASTER_KEY=${MEILI_MASTER_KEY:-brain-meili-key}
+      - BROWSERLESS_URL=http://brain-browserless:3000
+      - OPENAI_API_KEY=${OPENAI_API_KEY}
+      - OPENAI_MODEL=${OPENAI_MODEL:-gpt-4o-mini}
+      - TZ=${TZ:-America/Chicago}
+    depends_on:
+      brain-db:
+        condition: service_healthy
+      brain-redis:
+        condition: service_started
+
+  # ── PostgreSQL + pgvector ──
+  brain-db:
+    image: pgvector/pgvector:pg16
+    container_name: brain-db
+    restart: unless-stopped
+    environment:
+      - POSTGRES_USER=brain
+      - POSTGRES_PASSWORD=brain
+      - POSTGRES_DB=brain
+    volumes:
+      - ./data/postgres:/var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U brain"]
+      interval: 5s
+      timeout: 3s
+      retries: 10
+
+  # ── Redis ──
+  brain-redis:
+    image: redis:7-alpine
+    container_name: brain-redis
+    restart: unless-stopped
+    volumes:
+      - ./data/redis:/data
+
+  # ── Meilisearch ──
+  brain-meili:
+    image: getmeili/meilisearch:v1.12
+    container_name: brain-meili
+    restart: unless-stopped
+    environment:
+      - MEILI_MASTER_KEY=${MEILI_MASTER_KEY:-brain-meili-key}
+      - MEILI_ENV=production
+    volumes:
+      - ./data/meili:/meili_data
+
+  # ── Browserless (headless Chrome for JS rendering + screenshots) ──
+  brain-browserless:
+    image: ghcr.io/browserless/chromium:latest
+    container_name: brain-browserless
+    restart: unless-stopped
+    environment:
+      - MAX_CONCURRENT_SESSIONS=3
+      - TIMEOUT=30000
+
+networks:
+  pangolin:
+    external: true