Header/footer polish, fix dead link, add focus rings

- Dashboard header shortened to match every other page (was notably
  taller than the rest).
- Files moved before Settings in the bottom nav.
- Removed the header's course-name badge - purely redundant with the
  page's own heading directly below it.
- Fixed a dead link: "Progress" pointed to #stats, but no element
  with that id existed anywhere on the page.
- Added a visible :focus-visible ring across all pages - tabbing
  through the site previously gave no indication of what was focused.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -221,6 +221,11 @@ silently stay blank instead of erroring.
 - Grid view shows a small progress ring in the corner of each course's
   thumbnail (a checkmark once complete) instead of a separate bar, so
   completion reads at a glance without switching to list view
+- Interface polish: a shorter header (matching every other page instead of
+  standing out taller), Files moved before Settings in the bottom nav, a
+  visible focus ring for keyboard navigation, and a redundant course-name
+  badge removed from the header (the course name is already the page's own
+  heading right below it)
 
 **Playback & progress**
 - Video/audio player with resize, playback-speed presets, and resume-from-