feat: connect LiteLLM to AI PostgreSQL database

LiteLLM now uses the ai_postgres database instance with a dedicated
'litellm' database for API key management, usage tracking, and rate limiting.

Changes:
- Set DATABASE_URL to postgresql://ai:password@ai_postgres:5432/litellm
- Added depends_on ai_postgres to ensure DB starts first

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

ai/compose.yaml

@@ -96,10 +96,12 @@ services:
       TZ: ${TIMEZONE:-Europe/Berlin}
       ANTHROPIC_API_KEY: ${ANTHROPIC_API_KEY}
       LITELLM_MASTER_KEY: ${AI_LITELLM_API_KEY}
-      DATABASE_URL: null
+      DATABASE_URL: postgresql://${AI_DB_USER}:${AI_DB_PASSWORD}@ai_postgres:5432/litellm
     volumes:
       - ./litellm-config.yaml:/app/litellm-config.yaml:ro
     command: ["--config", "/app/litellm-config.yaml", "--host", "0.0.0.0", "--port", "4000", "--detailed_debug", "--drop_params"]
+    depends_on:
+      - ai_postgres
     networks:
       - compose_network
     healthcheck: