fix(channels): address R13 S3 review findings

- ActionMenu: skip disabled items in roving keyboard nav (plumb
  disabledIndices through the AnchoredPopover platform); a pending
  action no longer strands focus on an unfocusable button.
- ActionMenu + ChannelStatsPopover: add type="button" to the popover
  triggers so they can't submit an enclosing form.
- ChannelStatsPopover: restore the per-stat explanations as a native
  title on each row — the guidance the old inline stats showed is back.
- i18n: drop the now-dead channels.tags.yourTags / .manage keys (en+hu);
  the stats *Hint keys are live again via the restored row titles.
- test: cover ActionMenu (open/select/close/disabled) and
  ChannelStatsPopover (rows, conditional ETA row, per-row hint title).

frontend/src/components/AnchoredPopover.tsx

@@ -91,6 +91,9 @@ export interface AnchoredPopoverOptions {
    *  lands the roving focus on it instead of the first item — the behaviour a "pick one of these
    *  modes" menu needs. Leave unset for action menus and multi-select toggle lists. */
   selectedIndex?: number | null;
+  /** Indices of items that are disabled (e.g. an action whose mutation is already in flight), so
+   *  roving keyboard nav SKIPS them instead of stranding focus on an unfocusable disabled button. */
+  disabledIndices?: number[];
 }
 
 // Internal: call sites use the inferred hook return, they don't name the type.
@@ -175,6 +178,7 @@ export function useAnchoredPopover(opts: AnchoredPopoverOptions) {
       setHoverIndex(null);
     },
     selectedIndex: opts.selectedIndex ?? null,
+    disabledIndices: opts.disabledIndices,
     loop: true,
     // Focus the first item on open for BOTH click and keyboard (the default 'auto' skips pointer-opens,
     // which strands focus on the menu container — arrows then can't enter the roving list at all).