Labels: list, tag current, sync-to

- Tools -> Labels: list server labels, create/tag a label at current head,
  one-click Sync workspace to a label (via Get Revision)
- Backend p4 labels, p4 tag -l

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/p4.ts

@@ -65,6 +65,8 @@ export const p4 = {
   disconnect: () => invoke<void>("p4_disconnect"),
   sync: (scope = "") => invoke<string>("p4_sync", { scope }),
   syncTo: (scope: string, rev: string) => invoke<string>("p4_sync_to", { scope, rev }),
+  labels: () => invoke<{ label?: string; Update?: string; Owner?: string; Description?: string; [k: string]: unknown }[]>("p4_labels"),
+  labelTag: (label: string, scope: string, rev = "") => invoke<string>("p4_label_tag", { label, scope, rev }),
   diff: (file: string) => invoke<string>("p4_diff", { file }),
   revert: (files: string[]) => invoke<string>("p4_revert", { files }),
   submit: (description: string, files: string[]) =>