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

src/components/Popup.jsx

@@ -152,7 +152,7 @@ export default function Popup({
     <div className="popup">
       <div className="popup-inner" ref={rootRef}>
         <div className="popup-header drag-region">
-          <h1>Folder Bookmarks</h1>
+          <h1>Trailhead</h1>
           <div className="header-actions">
             {!creatingColumn ? (
               <button

src/styles/index.css

@@ -15,6 +15,19 @@
 
 * { box-sizing: border-box; }
 
+/* Hide scrollbars on every scroll surface. The popup still scrolls when
+   content exceeds the auto-resized window (or the columns row exceeds the
+   horizontal cap), but the chrome itself stays clean. */
+* {
+  scrollbar-width: none;
+  -ms-overflow-style: none;
+}
+*::-webkit-scrollbar {
+  width: 0;
+  height: 0;
+  display: none;
+}
+
 html, body, #root {
   margin: 0;
   padding: 0;