feat: squircle dock icon for macOS dev mode

macOS only applies the squircle mask to packaged .app bundles. For dev
mode, generate a pre-masked icon-dock.png via Swift/AppKit at launch
and set it with app.dock.setIcon(). Silently skipped on non-macOS.

packages/desktop/src/main.ts

@@ -513,6 +513,16 @@ if (!gotTheLock) {
   // ─── App Lifecycle ──────────────────────────────────────────────────────────
 
   app.whenReady().then(async () => {
+    // Set dock icon on macOS (overrides default Electron icon in dev mode)
+    if (process.platform === 'darwin' && app.dock) {
+      const dockIcon = path.join(__dirname, '..', 'build', 'icon-dock.png');
+      const fallbackIcon = path.join(__dirname, '..', 'build', 'icon.png');
+      const iconPath = fs.existsSync(dockIcon) ? dockIcon : fallbackIcon;
+      if (fs.existsSync(iconPath)) {
+        app.dock.setIcon(iconPath);
+      }
+    }
+
     // macOS application menu with "Change Instance"
     if (process.platform === 'darwin') {
       const appMenu = Menu.buildFromTemplate([