Move all completed items to Done section with commit hashes

BACKLOG.md

@@ -36,4 +36,18 @@ bottom as they come up.
 - [x] Surface yt-dlp extraction failures with a retry button.
 
 ## Done
-<!-- move completed items here with the commit hash -->
+- [x] Empty-state designs for empty playlists and empty history (match the new hero). `460aaae`
+- [x] Loading skeletons for search results instead of a bare "Searching…". `da2ad27`
+- [x] Keyboard-shortcut help overlay (press `?`), listing space / arrows / f / m. `c676786`
+- [x] Download/preload progress indicator on cards (percent or a bar, not just a pulse). `81aced9`
+- [x] Remember and restore the last playback position per video. `ddfa149`
+- [x] Toast queue (stack multiple toasts instead of replacing). `a4d6b82`
+- [x] Drag-to-reorder videos within a playlist. `0ba0f56`
+- [x] "Up next" queue panel showing the autoplay queue. `4376cd9`
+- [x] Persistent mini now-playing bar when browsing other views. `c1855a1`
+- [x] Cache size cap in Settings (auto-evict oldest past a limit). `d15d902`
+- [x] Export / import playlists as JSON. `d15d902`
+- [x] More / trending quick-search chips on the hero, rotated. `c6b8dfc`
+- [x] Sanitize `video_id` in `cache_download` (reject path separators). `c6b8dfc`
+- [x] Gate the embedded yt-dlp behind a build flag so debug builds compile faster. `d15d902`
+- [x] Surface yt-dlp extraction failures with a retry button. `c6b8dfc`