Preserve overlay across macOS flaps and mpv playlist changes

- keep visible overlays alive during transient macOS tracker loss
- reuse the running mpv overlay path on playlist navigation
- update regression coverage and changelog fragments

changes/323-macos-overlay-tracker-flaps.md

@@ -0,0 +1,4 @@
+type: fixed
+area: overlay
+
+- Kept the macOS visible overlay alive during transient mpv tracker flaps when the last tracked video geometry is still available.

changes/324-mpv-playlist-overlay-reuse.md

@@ -0,0 +1,4 @@
+type: fixed
+area: mpv
+
+- mpv: Playlist navigation now reuses the running SubMiner overlay without repeating the pause-until-ready warmup gate.