Add Favorites, storage drill-down, keyboard shortcuts, and What's New

- Favorites: star toggle on course rows, the course page, and a new
  dashboard card; rebased on rename/move, backed up/restored, and
  caught by stale-reference cleanup (also fixed a pre-existing gap
  where favorites.json wasn't in the backup file list).
- Storage Usage: click a folder row to drill into its contents one
  level at a time, with a Back button.
- Lesson player: added ,/. (speed step), [/] (prev/next lesson), and
  F (fullscreen) keyboard shortcuts.
- Settings: a CHANGELOG.md-backed "What's New" list, since VERSION
  alone only ever shows the current build.

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

CHANGELOG.md

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+2026-08-24 23:22 UTC — Add Favorites, storage drill-down, shortcuts, and What's New
+2026-08-24 19:00 UTC — Fix video resize handle drifting off-screen
+2026-08-24 18:06 UTC — Cache the category tree walk (fixes ~1s File Management page load)
+2026-08-24 14:41 UTC — Add search, bulk actions, undo, and storage usage to File Management
+2026-08-24 14:00 UTC — Fix build version showing "unknown" in production
+2026-08-24 13:52 UTC — Fix wrapped-course false positive in picker; add build version display
+2026-08-24 13:21 UTC — Exclude media-free subtrees from the destination picker too
+2026-08-24 13:13 UTC — Exclude course/item leaves from destination picker; ease new-folder UX
+2026-08-24 11:45 UTC — Add wildcard and regex modes to Bulk Rename
+2026-08-24 11:11 UTC — Add delete and ignore actions to Duplicate Courses
+2026-08-24 10:37 UTC — Move File Management link into the bottom tab bar
+2026-08-24 10:29 UTC — Tighten Sort Unsorted matching; consolidate file management tools
+2026-08-24 09:10 UTC — Add Unsorted folder auto-sort with keyword matching