android: a playlist file, picked

The storage plugin grew `pick_file` beside `pick_folder` and `pick_image`:
the document sheet with the caller's own filter, answered with a path Rust
can open. A document already on this phone hands its path over as it lies —
the document sibling of the same volume:relative id the folder picker
resolves, plus the Downloads provider's raw: — so a 300 MB pick copies
nothing; one that has no path is copied into cacheDir/picked under its own
name, and only as far as the caller allows, because a playlist is kilobytes
and a DJ set is not. Those copies are swept at the start of every pick,
which pick_image's never were.

The import sheet has its fifth door, on round 24's screen, wait card and
review, and the note that apologised for its absence says the one true thing
about it instead. `playlist_import_probe` took a path and a name the way
`playlist_import_folder` took a path, and the name is the load-bearing half:
the parser picks its format off the extension and titles the draft from the
stem, so a cache copy under an invented name would have read every playlist
as plain text. The mock walk drives the door and both of the picker's
refusals through round 31's fail door; the phone walk opens the real sheet
and dismisses it with BACK, reading nothing and writing nothing.

The brief asked for a second consumer — sending a file in a chat — and there
is nothing behind it: `community_pick_file` is the persona layer's three
native dialogs, `soulseek-client` has `say_room` and `message_user` and
nothing that sends a file, and both frontends' thread composers are text
only. Nothing was invented for it. The plugin command is general enough — a
caller's own filter, a zero-copy path, a bounded copy — that the one reader
still waiting, the local set listener the phone puts off by design, needs no
further plugin change. Playlist export is not on that list and never was:
writing a document out is the share plugin's errand, not a picker's. The
Kotlin is unbuilt — nothing on this machine compiles it.

src/mobile/HalfSheet.svelte

@@ -14,7 +14,7 @@
     import { streamSong, saveSong, streamCatalogAlbum, saveCatalogAlbum } from "./resolve.svelte.js";
     import { catalog, yearOf, artistKey, picture, heroFromPhoto, heroClear } from "./catalog.svelte.js";
     import { pls, bulk, bulkable, runBulk, coverFor, queueable, entryOf, playFrom, shufflePlay, togglePin, renamePlaylist, describePlaylist, duplicatePlaylist, deletePlaylist, removeItems, addEntries, createPlaylist, moveItem, coverFromPhoto, coverClear, EXPORTS, exportPlaylist } from "./playlists.svelte.js";
-    import { DOORS, start as startImport, pickImportFolder, startFolder } from "./importer.svelte.js";
+    import { DOORS, start as startImport, pickImportFolder, startFolder, pickImportFile, startFile } from "./importer.svelte.js";
     import { slsk, refreshRooms, disconnect, openThread, addBuddy, removeBuddy, leaveRoom } from "./slsk.svelte.js";
     import { lib, albumById, tracksOf, loadLibrary, refreshPlaylists } from "./lib.svelte.js";
     import { lyr, nudge, searchCandidates, closeCandidates, chooseCandidate, forgetLyrics, pasteLyrics, setAutoSync, openTapSync, tapProgress, reduceVocals, backToOriginal } from "./lyrics.svelte.js";
@@ -175,6 +175,18 @@
             onsubmit: (v) => { push("import", {}); void startImport(door, v); },
         });
     }
+    /* the playlist-file door picks FIRST too: the review only opens for a
+       file that was chosen, and a document this phone can hand no path for
+       is refused with the reason rather than half-read */
+    async function fileDoor() {
+        closeHalf();
+        try {
+            const picked = await pickImportFile();
+            if (!picked) return;
+            push("import", {});
+            void startFile(picked.path, picked.name);
+        } catch (e) { oops(e); }
+    }
     /* the folder door picks FIRST: the review only opens for a folder that
        was chosen, and a tree with no path on this phone cannot be walked */
     async function folderDoor() {
@@ -556,10 +568,10 @@
             <div class="sheet-title">Import a playlist</div>
             <div class="sheet-rows">
                 {#each DOORS as [door, icon, t, m] (door)}
-                    {@render row(icon, t, m, () => (door === "folder" ? folderDoor() : importPrompt(door)))}
+                    {@render row(icon, t, m, () => (door === "folder" ? folderDoor() : door === "file" ? fileDoor() : importPrompt(door)))}
                 {/each}
             </div>
-            <div class="sec-note" style="padding-bottom: 14px">A playlist file — M3U, XSPF, PLS or CSV — imports on the desktop; the phone has no file picker for one yet.</div>
+            <div class="sec-note" style="padding-bottom: 14px">A playlist file's rows are matched against the library on this phone — by path where the file names one, and by filename otherwise, so a file copied here from another machine still finds what you have.</div>
         {:else if kind === "plmatch" && shown?.arg?.item}
             {@const p = shown.arg.playlist}
             {@const item = shown.arg.item}