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.tsx

@@ -23,6 +23,7 @@ export function useChannelActions({
   onView,
   onOpenWizard,
   tags,
+  tagsState = "ready",
   onToggleTag,
   onPickPriority,
 }: {
@@ -30,6 +31,9 @@ export function useChannelActions({
   onOpenWizard: () => void;
   /** The reader's own tags (no system tags) — the Tags submenu lists them A–Z. */
   tags: readonly Tag[];
+  /** Whether `tags` is the answer yet: loading or failed is said as such, never as "no tags yet"
+   *  (E28 review J3). */
+  tagsState?: "loading" | "error" | "ready";
   onToggleTag: (c: ManagedChannel, tagId: number) => void;
   /** A priority step picked: the caller re-sorts its list and follows the row. */
   onPickPriority: (c: ManagedChannel, priority: number) => void;
@@ -149,8 +153,15 @@ export function useChannelActions({
       label: t("channels.tags.label"),
       icon: <Tags className="w-4 h-4" />,
     };
-    if (tags.length === 0)
-      return { ...base, disabled: true, note: t("channels.row.noTagsYet"), onSelect: () => {} };
+    if (tags.length === 0) {
+      const note =
+        tagsState === "loading"
+          ? t("common.loading")
+          : tagsState === "error"
+            ? t("common.loadError")
+            : t("channels.row.noTagsYet");
+      return { ...base, disabled: true, note, onSelect: () => {} };
+    }
     const on = new Set(c.tag_ids);
     return {
       ...base,