fix(ui): a picker whose list failed says so, and takes no pick while one is being written

- Combobox gains `error` (said in the list, not "No matches") and a soft `disabled` (keeps the
  focus, announced, opens and changes nothing).
- UserPicker passes both: the share dialog's recipient picker is off while a share is pending, and
  the share and quota pickers say when the user list failed to load.
- ChannelPicker and the Plex playlist/collection pickers say a failed load too.
- The channel menu's Tags row says loading / failed instead of "no tags yet".

frontend/src/components/useChannelActions.dom.test.tsx

@@ -40,6 +40,7 @@ afterEach(() => {
   h.role = "user";
   h.canWrite = true;
   tags = [];
+  tagsState = "ready";
   onToggleTag.mockReset();
   onPickPriority.mockReset();
 });
@@ -70,6 +71,7 @@ const onView = vi.fn();
 const onToggleTag = vi.fn();
 const onPickPriority = vi.fn();
 let tags: Tag[] = [];
+let tagsState: "loading" | "error" | "ready" = "ready";
 const tag = (id: number, name: string) => ({ id, name }) as Tag;
 function mount() {
   const qc = new QueryClient({ defaultOptions: { mutations: { retry: false } } });
@@ -77,7 +79,15 @@ function mount() {
     <QueryClientProvider client={qc}>{children}</QueryClientProvider>
   );
   return renderHook(
-    () => useChannelActions({ onView, onOpenWizard: () => {}, tags, onToggleTag, onPickPriority }),
+    () =>
+      useChannelActions({
+        onView,
+        onOpenWizard: () => {},
+        tags,
+        tagsState,
+        onToggleTag,
+        onPickPriority,
+      }),
     { wrapper },
   );
 }
@@ -220,6 +230,14 @@ describe("useChannelActions — the Tags submenu", () => {
     expect(onToggleTag).toHaveBeenCalledWith(expect.objectContaining({ id: "UC1" }), 2);
   });
 
+  // E28 review J3: a failed /tags read said "no tags yet" — an error dressed as an empty list.
+  it("says the tags are loading, or failed to load, instead of 'no tags yet'", () => {
+    tagsState = "loading";
+    expect(row(ch(), "tags")).toMatchObject({ disabled: true, note: "common.loading" });
+    tagsState = "error";
+    expect(row(ch(), "tags")).toMatchObject({ disabled: true, note: "common.loadError" });
+  });
+
   it("stays in place, off, saying where tags are made, with no tag yet", () => {
     expect(row(ch(), "tags")).toMatchObject({ disabled: true, note: "channels.row.noTagsYet" });
     expect(row(ch(), "tags").items).toBeUndefined();