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>

gateway/sessions.py

@@ -4,8 +4,9 @@ Platform Gateway — Session and service-connection helpers.
 
 import secrets
 from datetime import datetime, timedelta
+import bcrypt
 
-from config import SESSION_MAX_AGE
+from config import SESSION_MAX_AGE, DEV_AUTO_LOGIN_USERNAME, DEV_AUTO_LOGIN_DISPLAY_NAME
 from database import get_db
 
 
@@ -52,6 +53,24 @@ def get_service_token(user_id, service):
     return dict(row) if row else None
 
 
+def get_or_create_dev_user():
+    conn = get_db()
+    row = conn.execute("SELECT * FROM users WHERE username = ?", (DEV_AUTO_LOGIN_USERNAME,)).fetchone()
+    if row:
+        conn.close()
+        return dict(row)
+
+    pw_hash = bcrypt.hashpw(secrets.token_hex(16).encode(), bcrypt.gensalt()).decode()
+    conn.execute(
+        "INSERT INTO users (username, password_hash, display_name) VALUES (?, ?, ?)",
+        (DEV_AUTO_LOGIN_USERNAME, pw_hash, DEV_AUTO_LOGIN_DISPLAY_NAME)
+    )
+    conn.commit()
+    row = conn.execute("SELECT * FROM users WHERE username = ?", (DEV_AUTO_LOGIN_USERNAME,)).fetchone()
+    conn.close()
+    return dict(row) if row else None
+
+
 def set_service_token(user_id, service, auth_token, auth_type="bearer"):
     conn = get_db()
     conn.execute("""