import: the whole feature, and releases put back together

Everything the import grew over the last week, landing in one go — the
window, the picker, the audition pen, apply, and the review that stands
between them.

The fold is the new part. A release filed as a container of parts arrived
as N albums, because the scan groups audio by its immediate parent and the
container holds none of its own: Analord's eleven volumes were eleven
records, and six more releases split the same way. Records now fold into
the release above them, and apply is handed an explicit part list — never a
recursive walk, which is what let one stray file swallow 288 descendants
and duplicate 9 GB.

Where releases live is read off the collection rather than assumed, so a
genre-nested library moves the answer instead of breaking; below a dominant
majority at one depth the pass refuses entirely, because no folding beats
wrong folding. Three vetoes independent of depth catch a misread level.
Every fold is listed in the review with a way out.

research/import/fold-audit.mjs imports the shipping module, so the audited
code is the running code: 9 folds, 0 swallows across four library shapes,
and none of the 148 artist folders touched. It was that harness that killed
the tempting version of this rule — matching a part against its container
folded 40 artist folders, Mac Demarco's 8 albums into one, because album
folders carry the artist's name.

The regression test found a live bug on the way: parts number from 01 each,
so flattening two discs collided, and "same name, same size" read the
second file as already-imported and dropped it while still counting it.
That reuse now also requires that this run has not already written the
path.

Also here: the picker's accent crossfades between records instead of
cutting through the app's blue (ownership moved to the window, which
survives the per-record re-key), the fullscreen viewer wears the album's
accent instead of the one it left behind in the portal, Skip defers a
record without deciding it, and Keep mine is gone — with the cards picked
field by field it was Next under another name.

crates/soulseek-client/src/transfer.rs

@@ -57,10 +57,15 @@ pub(crate) fn start_download(
     filename: &str,
     size: u64,
     target: Option<PathBuf>,
+    claim: impl FnOnce(u64),
 ) -> u64 {
     let id = inner
         .download_counter
         .fetch_add(1, std::sync::atomic::Ordering::Relaxed);
+    // Before the spawn below, never after: the task's first act is to emit
+    // Connecting, and a listener that has not yet claimed this id cannot tell
+    // the event is theirs.
+    claim(id);
     let cancel = CancellationToken::new();
     inner.downloads_by_file.lock().unwrap().insert(
         (username.to_string(), filename.to_string()),
@@ -362,6 +367,11 @@ impl Download {
             None => ("", self.filename.as_str()),
         };
         let mut dir = self.inner.downloads_dir.clone();
+        // Staging lives in ONE visible pen — "(Cache)" — never loose in the
+        // library root: a half-finished transfer is not a record, and a
+        // peer's username is not an artist. organize_download lifts the
+        // finished file out; cleanup_staging tidies what it leaves behind.
+        dir.push("(Cache)");
         dir.push(sanitize(&self.username));
         if !folder.is_empty() {
             dir.push(sanitize(folder));