feat(ui): showcase github projects and link service cards

[Adiker]

Summary

• Add a selected GitHub projects section with the four pinned repositories first and the featured LiMusic fork last.
• Make each project card and each web service detail card a full-card link with a consistent arrow indicator.
• Add English and Polish copy, theme-aware styles, and documentation.

Verification

• node --check js/app.js
• PYTHONDONTWRITEBYTECODE=1 python3 -m unittest discover -s ops/muse-status -p 'test_*.py' (8 tests)
• git diff --check
• Local HTTP and browser checks: assets and links, 320/390 px layouts, Dark/Light/OLED themes, EN/PL content, keyboard tab navigation, and visible focus.

Risk and rollback

This changes how the service and project cards open external pages. If the interaction regresses, revert the PR merge commit.