feat: merge temp cleanup on close + v1.4 changelog + README (Phase 2)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

main.py

@@ -5031,9 +5031,17 @@ class MainWindow(QMainWindow):
 
     # ── Changelog ────────────────────────────────────────────
 
-    APP_VERSION = "1.3"
+    APP_VERSION = "1.4"
     _SPLIT_HEADER_H = 22  # deck split-column header height (keep both deck spots in sync)
     CHANGELOG: list[tuple[str, list[str]]] = [
+        ("1.4", [
+            "<b>Merge (crossfade)</b> — a new <b>Merge</b> pane in the Audio tab "
+            "assembles multiple clips into one, crossfading every join. Add the "
+            "current audio area (with its edits) or files from disk, reorder or "
+            "remove them, set the crossfade length, then <b>Preview</b> to "
+            "audition or <b>Merge &amp; Save</b> to render. Clips shorter than "
+            "the crossfade are flagged before rendering.",
+        ]),
         ("1.3", [
             "<b>Audio workspace tab</b> — the <b>Scan</b> control-deck tab is "
             "now <b>Audio</b>, a <code>QToolBox</code> with two panes. "
@@ -8646,6 +8654,14 @@ class MainWindow(QMainWindow):
 
     def closeEvent(self, event):
         _log("Shutting down…")
+        # Stop any running audition and clean up merge temp WAVs.
+        self._stop_audition()
+        for _t in list(self._merge_temps):
+            try:
+                os.remove(_t)
+            except OSError:
+                pass
+        self._merge_temps.clear()
         # Save file-list tabs for resume (per-profile).
         self._save_playlist_tabs()
         # Cancel background workers to prevent callbacks into dead objects.