Fix EXPOSE to use explicit port 7242

Update Dockerfile to use ARG APP_PORT and ENV properly

Add app_port: 7242 to Docker Space frontmatter

Remove app_file from Docker Space frontmatter

Fix README frontmatter to match exact template format

Align README frontmatter with checker template (app_file, pinned)

Reset sdk: docker with app_port

Temporarily set sdk: gradio to force Hub re-parse

Add sdk_version and pinned to README frontmatter

Set Space title to exact 'ga2-3d239e'

Initial deployment: ga2-3d239e Docker Space (FastAPI on 7242)