fix: restore sdk_version 6.18.0 (gr.Server needs Gradio 6+)

fix: app_file → app.py

docs: add YouTube demo link, badges, capabilities

fix: sdk_version 6.18.0 (required for gr.Server)

docs: add GGUF section, update badges to 6/6, add local run instructions

Upload README.md with huggingface_hub

Upload README.md with huggingface_hub

initial commit