feat: wire brain service to platform gateway

- Gateway proxies /api/brain/* to brain-api:8200/api/* via pangolin network
- User identity injected via X-Gateway-User-Id header
- Brain app registered in gateway database (sort_order 9)
- Added to GATEWAY_KEY_SERVICES for dashboard integration
- Tested: health, config, list, create all working through gateway

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

gateway/database.py

@@ -8,7 +8,7 @@ import bcrypt
 
 from config import (
     DB_PATH, TRIPS_URL, FITNESS_URL, INVENTORY_URL,
-    MINIFLUX_URL, SHELFMARK_URL, SPOTIZERR_URL, BUDGET_URL, TASKS_URL,
+    MINIFLUX_URL, SHELFMARK_URL, SPOTIZERR_URL, BUDGET_URL, TASKS_URL, BRAIN_URL,
 )
 
 
@@ -129,6 +129,13 @@ def init_db():
         conn.commit()
         print("[Gateway] Added tasks app")
 
+    # Ensure brain app exists
+    brain = c.execute("SELECT id FROM apps WHERE id = 'brain'").fetchone()
+    if not brain:
+        c.execute("INSERT INTO apps VALUES ('brain', 'Brain', 'brain', '/brain', ?, 9, 1, NULL)", (BRAIN_URL,))
+        conn.commit()
+        print("[Gateway] Added brain app")
+
     # Seed admin user from env vars if no users exist
     import os
     user_count = c.execute("SELECT COUNT(*) FROM users").fetchone()[0]