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/library/src/lib.rs

@@ -748,6 +748,19 @@ impl Library {
         Ok(rows.filter_map(|r| r.ok()).collect())
     }
 
+    /// Drop specific track rows by id. Used when the import tool replaces an
+    /// album's audio with another version: the rows for the copy that was
+    /// replaced go with its files. The album row is deliberately left alone —
+    /// the caller is mid-apply and has already registered the replacement.
+    pub fn remove_tracks(&self, ids: &[i64]) -> Result<usize> {
+        let conn = self.conn.lock().unwrap();
+        let mut removed = 0;
+        for id in ids {
+            removed += conn.execute("DELETE FROM tracks WHERE id = ?1", [id])?;
+        }
+        Ok(removed)
+    }
+
     /// Paths of tracks missing the audio-props backfill (size is the sentinel:
     /// always available from the filesystem, so a non-null size means scanned).
     pub fn tracks_missing_props(&self) -> Result<Vec<(i64, String)>> {