fix(desktop): use repo-forked codicon (git-fork has no glyph)

The bundled @vscode/codicons font has no `git-fork` glyph (only
`git-fork-private`), so the Branch menu item rendered blank. Use
`repo-forked`, the actual fork icon, to match the inline GitFork action.

apps/desktop/src/app/chat/sidebar/session-actions-menu.tsx

@@ -273,8 +273,10 @@ function useSessionActions({
   const workItems: ItemSpec[] = [
     spec({
       disabled: !onBranch,
-      // Match the inline message action's GitFork icon (assistant-message.tsx).
-      icon: 'git-fork',
+      // Fork glyph to match the inline message action's GitFork icon
+      // (assistant-message.tsx). NB: this codicon font has no `git-fork`
+      // glyph (only `git-fork-private`); `repo-forked` is the fork icon.
+      icon: 'repo-forked',
       label: r.branchFrom,
       onSelect: () => {
         triggerHaptic('selection')