add a one-step undo and harden queue edits

docs/architecture.md

@@ -88,7 +88,7 @@ Because the resolver reports *which entry* a position falls in, `PlaybackState`
 
 Stream URLs come from `SourceRepository.streamUri`, which asks the active `SubsonicSource` for a freshly salted `stream` URL; because the URL changes every request, artwork is attached to the media item by identity (the `CoverArtRef` cache key) rather than by URL.
 
-The window is also the queue the media notification and Android Auto can browse — a deliberate trade-off, since the alternative is holding an entire large library in memory. The queue view resolves positions lazily too: it pages with queries bounded to one page per entry (never the whole queue) and rewrites `queue_entries` to edit. Removing a position splits its entry into up to two ranges, and moving one turns the moved track into an explicit song entry inserted at the target index, so an edit costs a couple of rows rather than a copy of the queue. When the edit falls inside the player's window the controller mirrors it with `removeMediaItem`/`moveMediaItem` so playback is not interrupted; a move that crosses the window boundary reloads the window around the cursor at the current position. Timed lyrics/gapless format preferences, scrobbling, downloads and adding to the queue from the library are not wired yet.
+The window is also the queue the media notification and Android Auto can browse — a deliberate trade-off, since the alternative is holding an entire large library in memory. The queue view resolves positions lazily too: it pages with queries bounded to one page per entry (never the whole queue) and rewrites `queue_entries` to edit. Removing a position splits its entry into up to two ranges, and moving one turns the moved track into an explicit song entry inserted at the target index, so an edit costs a couple of rows rather than a copy of the queue. When the edit falls inside the player's window the controller mirrors it with `removeMediaItem`/`moveMediaItem` so playback is not interrupted; removing the playing track, or a move that crosses the window boundary, reloads the window around the cursor. The controller keeps the pre-edit entries and cursor, so the queue view can offer a one-step undo. Timed lyrics/gapless format preferences, scrobbling, downloads and adding to the queue from the library are not wired yet.
 
 ## Data model
 

docs/implementation-plan.md

@@ -35,7 +35,7 @@ Not done yet in this slice (deliberately): artist detail, cover-art tonal colour
 - (done) A SQL-backed queue of references (whole playlist / album / song, each with an optional ordinal range) resolved lazily, with only a bounded window in memory and in the player.
 - (done) Streaming bitrate and preferred format from settings (`maxBitRate`/`format`, so the server transcodes as configured).
 - (done) Playing from the Songs tab: the tapped song queues the whole songs list at that position.
-- (done) A queue view that lists the resolved queue, jumps to a track on tap, removes tracks and reorders them by dragging.
+- (done) A queue view that lists the resolved queue, jumps to a track on tap, removes tracks and reorders them by dragging, with a one-step undo.
 - Adding to the queue from the library (play next / add to queue), and gapless format preferences.
 - Scrobbling and "now playing" back to the server.
 - Optional download/caching.