fix(branch-selector): show loading state instead of "No branches"

[ryans-posthog]

Summary

When the branch list in the branch selector is loading, the dropdown previously showed "No branches found." next to the trigger spinner — confusing UX implying the repo had no branches. This change surfaces a dedicated "Loading branches…" row while the fetch is in flight, so the empty state only appears once the query completes.

• Captured the previously discarded isLoading flag from the local-mode getAllBranches query.
• Combined local + cloud loading sources into a single branchListLoading flag.
• Replaced the always-on <ComboboxEmpty> with a conditional that renders an inline spinner + "Loading branches…" row (mirroring the existing "Loading more (N)…" pattern) while loading and empty, falling back to "No branches found." otherwise so search filtering still works.

Test plan

• Open branch selector on a fresh local repo — verify "Loading branches…" row appears, then list populates.
• Open branch selector in cloud mode — verify same loading row, then branches populate.
• Type a query that matches no branches after load — verify "No branches found." still shows.
• Open branch selector when branches are already cached — verify no flash of loading row.

Generated-By: PostHog Code
Task-Id: 322fe270-1290-4c9d-b505-1eed6961381f

[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
apps/code/src/renderer/features/git-interaction/components/BranchSelector.tsx:258-261
**Duplicated loading-row markup (OnceAndOnlyOnce)**

The new "Loading branches…" row (lines 258–261) has identical structure to the existing "Loading more (N)…" row at lines 251–254 — same `div` className, same `Spinner` props, same layout. Since both are in the same file, extracting a tiny shared helper keeps the pattern in one place and makes future style changes (e.g. icon size, padding) trivially consistent.

Consider extracting:
```tsx
function LoadingRow({ label }: { label: string }): JSX.Element {
  return (
    <div className="flex items-center gap-1 px-2 py-1.5 text-muted-foreground text-xs">
      <Spinner size={12} className="animate-spin" />
      {label}
    </div>
  );
}
```
Then replace both occurrences with `<LoadingRow label="Loading branches…" />` and `<LoadingRow label={\`Loading more (${branches.length})…\`} />`.

_{Reviews (1): Last reviewed commit: "fix(branch-selector): show loading state..." | Re-trigger Greptile}