Eight usability additions on top of the mobile redesign: course cover-image
thumbnails, a debounced library search, a Continue Watching section split
from Recently Viewed, per-lesson playback speed control, an installable
PWA manifest/icons, name sort in the library browser, per-lesson notes, and
a bulk mark-course-as-watched action. Also fixes two real bugs found along
the way: lesson_view.html was missing the viewport meta tag (so lesson
pages weren't actually mobile-responsive), and update_lesson_progress
always overwrote the whole progress entry, which would have silently
deleted a saved note on the next routine autosave.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
