Move the large inline HTML template from settings.go into a separate
file at internal/templates/settings.html, matching the project convention
used by all other handlers. The template is now loaded at render time
via template.ParseFiles, consistent with dashboard, issues, etc.
Closesleeworks-agents/gitea-mobile#126
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>