Rebrand to Trailhead

- Tray tooltip: "Trailhead Path Bookmarker"
- Popup header: "Trailhead"
- electron-builder productName: "Trailhead"
- New tray icon: orange mountain peak with pennant flag (replaces folder
  pictogram). Tuned to 2px-min strokes so it survives downscaling to the
  16-24px Windows tray
- Hide scrollbars across all scroll surfaces (popup, columns row, tab
  strip) while keeping scroll behavior intact

electron/main.js

@@ -471,7 +471,7 @@ function addBookmarkInternal({ id, alias, path: pathValue, color, columnId, hide
 function createTray() {
   const image = nativeImage.createFromPath(getIconPath());
   tray = new Tray(image.isEmpty() ? nativeImage.createEmpty() : image);
-  tray.setToolTip('Folder Bookmark Tray');
+  tray.setToolTip('Trailhead Path Bookmarker');
   tray.setContextMenu(buildContextMenu());
   tray.on('click', togglePopup);
 }