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-tauri/src/lib.rs

@@ -485,6 +485,30 @@ async fn p4_sync(state: State<'_, AppState>, scope: String) -> Result<String, St
     Ok(if msg.is_empty() { "Already up to date — nothing to sync.".into() } else { msg })
 }
 
+/// List labels on the server (most-recently-updated first).
+#[tauri::command]
+async fn p4_labels(state: State<'_, AppState>) -> Result<Vec<Value>, String> {
+    let conn = current(&state)?;
+    run_json(&conn, &["labels", "-m", "300"])
+}
+
+/// Tag revisions with a label (auto-creates the label if new). `rev` optional:
+/// a changelist, another label, or a date; empty = head. Scope confines it.
+#[tauri::command]
+async fn p4_label_tag(state: State<'_, AppState>, label: String, scope: String, rev: String) -> Result<String, String> {
+    let conn = current(&state)?;
+    let label = label.trim();
+    if label.is_empty() {
+        return Err("No label name".into());
+    }
+    let mut spec = scope_spec(&scope);
+    let rev = rev.trim().trim_start_matches(['@', '#']);
+    if !rev.is_empty() {
+        spec = format!("{spec}@{rev}");
+    }
+    run_text(&conn, &["tag", "-l", label, &spec])
+}
+
 /// Sync the workspace to an exact revision: a changelist number, a label name,
 /// or a date (`YYYY/MM/DD`). `rev` is appended to the scope spec as `@rev`.
 #[tauri::command]
@@ -2058,6 +2082,8 @@ pub fn run() {
             p4_typemap_set,
             p4_reopen_type,
             p4_sync_to,
+            p4_labels,
+            p4_label_tag,
             p4_client_spec,
             p4_client_save,
             uasset_thumbnail,