feat(overlay): add in-app changelog modal

- Add a changelog modal opened from tray "View Changelog" or the update notification's "What's New" button; renders in-player or in its own window like the help modal
- Fetch changelog from the newest published release so newer-than-installed notes are visible, falling back to the bundled CHANGELOG.md on failure
- Group versions by minor line (current expanded, older folded), badge the installed version, tag newer ones "New"
- Support J/K/arrow navigation, Enter to fold/unfold, R to refetch, Esc to close
- Add changelog parsing/semver-compare utils and changelog IPC channel/runtime; bundle CHANGELOG.md into packaged builds
- Replace release/release-notes.md with changes/changelog-modal.md changeset entry

src/renderer/overlay-notifications.ts

@@ -293,7 +293,9 @@ export function createOverlayNotificationRenderer(
           window.electronAPI.sendOverlayNotificationAction?.(entry.id, action.id, {
             noteId: action.noteId,
           });
-          remove(entry.id);
+          if (action.keepOpen !== true) {
+            remove(entry.id);
+          }
         });
         actions.append(button);
       }