feat: add Flux image generation function for Open WebUI

- Add flux_image_gen.py manifold function for Flux.1 Schnell
- Auto-mount functions via Docker volume (./functions:/app/backend/data/functions:ro)
- Add comprehensive setup guide in FLUX_SETUP.md
- Update CLAUDE.md with Flux integration documentation
- Infrastructure as code approach - no manual import needed

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

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

ai/compose.yaml

@@ -66,6 +66,7 @@ services:
 
     volumes:
       - ai_webui_data:/app/backend/data
+      - ./functions:/app/backend/data/functions:ro
     depends_on:
       - ai_postgres
       - litellm