android: a playlist's cover from a photo on the phone

The storage plugin gains pick_image — the document picker limited to
images, the picked content copied into the app's cache so the Rust side
gets a plain path. playlist_cover_set(id, path) is the desktop pick's
install step split out and shared (squared, the master cover, the row's
revision moved). A playlist's sheet offers Choose cover photo and Remove
custom cover; the mock walk exercises both.

src/lib/api.js

@@ -274,6 +274,7 @@ export const playlistCover = (id, maxEdge = null) =>
     invoke("playlist_cover", { id, maxEdge });
 export const playlistCoverPick = (id) => invoke("playlist_cover_pick", { id });
 export const playlistCoverClear = (id) => invoke("playlist_cover_clear", { id });
+export const playlistCoverSet = (id, path) => invoke("playlist_cover_set", { id, path });
 // Import: probe opens a file dialog and stages a reviewed draft; text stages
 // a pasted tracklist; commit writes the accepted draft in one transaction.
 export const playlistImportProbe = () => invoke("playlist_import_probe");
@@ -500,6 +501,8 @@ export const requestAllFilesAccess = () => invoke("plugin:storage|request_all_fi
 // The phone's share plugin (crates/tauri-plugin-share): what another app
 // shared to SoulStream, { text } — read once.
 export const pendingShare = () => invoke("plugin:share|pending_share");
+// A photo from the phone (the storage plugin): { path } in the app's cache.
+export const pickImage = () => invoke("plugin:storage|pick_image");
 // Download a found album copy into (Cache)\_audition\<rel>\ for the version
 // comparison. Called track 1 first, then the rest — `startIndex` keeps the
 // second batch's indices continuing, since index 0 means "track 1".