feat: expose LiteLLM publicly for Codex CLI integration

Added Traefik configuration to make LiteLLM accessible at llm.ai.pivoine.art
for use with @openai/codex CLI tool.

Changes:
- Added AI_LITELLM_TRAEFIK_HOST to arty.yml (llm.ai.pivoine.art)
- Updated ai/compose.yaml litellm service with full Traefik labels
- HTTP to HTTPS redirect
- SSL termination via Let's Encrypt
- Compression and security headers

This allows external tools like Codex to use Claude models via
OpenAI-compatible API endpoint.

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

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

arty.yml

@@ -182,6 +182,7 @@ envs:
     AI_VECTOR_DB: pgvector
     AI_CRAWL4AI_PORT: 11235
     AI_OPENAI_API_BASE_URLS: https://api.anthropic.com/v1
+    AI_LITELLM_TRAEFIK_HOST: llm.ai.pivoine.art
     # Asciinema
     ASCIINEMA_TRAEFIK_ENABLED: true
     ASCIINEMA_COMPOSE_PROJECT_NAME: asciinema