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/models/item.py

@@ -0,0 +1,80 @@
+"""SQLAlchemy models for the brain service."""
+
+import uuid
+from datetime import datetime
+
+from pgvector.sqlalchemy import Vector
+from sqlalchemy import (
+    Column, String, Text, Integer, Float, DateTime, ForeignKey, Index, text
+)
+from sqlalchemy.dialects.postgresql import JSONB, UUID, ARRAY
+from sqlalchemy.orm import relationship
+
+from app.config import OPENAI_EMBED_DIM
+from app.database import Base
+
+
+def new_id():
+    return str(uuid.uuid4())
+
+
+class Item(Base):
+    __tablename__ = "items"
+
+    id = Column(UUID(as_uuid=False), primary_key=True, default=new_id)
+    user_id = Column(String(64), nullable=False, index=True)
+    type = Column(String(32), nullable=False, default="link")  # link|note|pdf|image|document|file
+    title = Column(Text, nullable=True)
+    url = Column(Text, nullable=True)
+    raw_content = Column(Text, nullable=True)       # original user input (note body, etc.)
+    extracted_text = Column(Text, nullable=True)     # full extracted text from page/doc
+    folder = Column(String(64), nullable=True)
+    tags = Column(ARRAY(String), nullable=True, default=list)
+    summary = Column(Text, nullable=True)
+    confidence = Column(Float, nullable=True)
+    metadata_json = Column(JSONB, nullable=True, default=dict)
+    processing_status = Column(String(32), nullable=False, default="pending")  # pending|processing|ready|failed
+    processing_error = Column(Text, nullable=True)
+
+    # Embedding (pgvector)
+    embedding = Column(Vector(OPENAI_EMBED_DIM), nullable=True)
+
+    created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
+    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow, nullable=False)
+
+    # Relationships
+    assets = relationship("ItemAsset", back_populates="item", cascade="all, delete-orphan")
+
+    __table_args__ = (
+        Index("ix_items_user_status", "user_id", "processing_status"),
+        Index("ix_items_user_folder", "user_id", "folder"),
+        Index("ix_items_created", "created_at"),
+    )
+
+
+class ItemAsset(Base):
+    __tablename__ = "item_assets"
+
+    id = Column(UUID(as_uuid=False), primary_key=True, default=new_id)
+    item_id = Column(UUID(as_uuid=False), ForeignKey("items.id", ondelete="CASCADE"), nullable=False, index=True)
+    asset_type = Column(String(32), nullable=False)  # screenshot|archived_html|original_upload|extracted_file
+    filename = Column(String(512), nullable=False)
+    content_type = Column(String(128), nullable=True)
+    size_bytes = Column(Integer, nullable=True)
+    storage_path = Column(String(1024), nullable=False)  # relative path in storage
+
+    created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
+
+    # Relationships
+    item = relationship("Item", back_populates="assets")
+
+
+class AppLink(Base):
+    """Placeholder for future cross-app linking (e.g. link a saved item to a trip or task)."""
+    __tablename__ = "app_links"
+
+    id = Column(UUID(as_uuid=False), primary_key=True, default=new_id)
+    item_id = Column(UUID(as_uuid=False), ForeignKey("items.id", ondelete="CASCADE"), nullable=False, index=True)
+    app = Column(String(64), nullable=False)       # trips|tasks|fitness|inventory
+    app_entity_id = Column(String(128), nullable=False)
+    created_at = Column(DateTime, default=datetime.utcnow, nullable=False)