Lyrics Card Generator v6.2.9

Internal cleanup and maintenance

Remove unused components, color analysis, character-based height estimation and obsolete styles while preserving the existing interface and features.
Remove an unused development dependency, a duplicate icon source and uncalled test helpers.
Use one desktop packaging file list and a shared browser test server while retaining history compatibility, automatic drafts, export and security checks.

This change only cleans up internal implementation. Fonts, languages, accessibility, historical data and export behavior remain unchanged.