Replaces the hand-written Tailwind subset in app.css with a real, purged
Tailwind build: scripts/build_css.py runs the pinned, SHA-256-checked
standalone Tailwind CLI (no Node), the generated tailwind.css and
plugin-frame.css are committed, and CI fails when they are stale. The Pi
never builds anything. The login page (#683) now links tailwind.css too,
and the load-order test covers every template that links app.css.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
