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

package.json

@@ -29,7 +29,7 @@
   },
   "build": {
     "appId": "com.dbeuttel.folder-bookmark-tray",
-    "productName": "Folder Bookmark Tray",
+    "productName": "Trailhead",
     "files": [
       "electron/**/*",
       "dist/**/*",