Apply code formatting and fix compatibility issues

Fix Hugging Face cache path configuration for Spaces

Remove all FLUX references and use only SDXL models

Use SDXL-Turbo on HF Spaces to avoid permission errors

Auto-disable FLUX on Hugging Face Spaces to prevent access errors

Make it run locally with new sdxl-base model

Switch primary model from FLUX to SDXL for better reliability

Add modern Python development toolchain with Ruff, MyPy, and pre-commit

Migrate entire codebase from SDXL-Turbo to FLUX.1-schnell

Refactor the app to be more modular