feat: integrate Facefusion into AI stack

Added Facefusion face swapping service to the AI stack:

**Configuration:**
- URL: https://facefusion.ai.pivoine.art
- Image: facefusion/facefusion:3.5.0-cpu
- Port: 7865
- Container: ai_facefusion
- Volume: ai_facefusion_data
- HTTP Basic Auth protection
- CPU execution mode (GPU when available)

**Changes:**
- Added facefusion service to ai/compose.yaml
- Added AI_FACEFUSION_* env vars to arty.yml
- Created ai_facefusion_data volume
- Removed old standalone facefusion stack
- Removed ai/README-export.md and ai/webui-export.py

Facefusion will run on CPU until GPU server is available.

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

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

arty.yml

@@ -170,6 +170,10 @@ envs:
     AI_POSTGRES_IMAGE: pgvector/pgvector:pg16
     AI_WEBUI_IMAGE: ghcr.io/open-webui/open-webui:main
     AI_CRAWL4AI_IMAGE: unclecode/crawl4ai:latest
+    AI_FACEFUSION_IMAGE: facefusion/facefusion:3.5.0-cpu
+    AI_FACEFUSION_TRAEFIK_ENABLED: true
+    AI_FACEFUSION_TRAEFIK_HOST: facefusion.ai.pivoine.art
+    AI_FACEFUSION_EXECUTION_PROVIDERS: cpu
     AI_TRAEFIK_HOST: ai.pivoine.art
     AI_DB_USER: ai
     AI_DB_NAME: openwebui