fix(feed): clamp the view menu's roving index to the option list

Guards the shared switcher against a caller whose option list shrinks
while the menu is open, which would leave every item un-tabbable.

frontend/src/components/ViewSwitcher.tsx

@@ -54,9 +54,12 @@ export default function ViewSwitcher<T extends string>({
     setFocusIdx(currentIdx);
     setOpen(true);
   }
+  // Clamped at render, so a caller whose option list shrinks while the menu is open can't leave
+  // the roving tabindex pointing past the end (which would make every item un-tabbable).
+  const rovingIdx = Math.min(focusIdx, options.length - 1);
   useEffect(() => {
-    if (open) itemRefs.current[focusIdx]?.focus();
-  }, [open, focusIdx]);
+    if (open) itemRefs.current[rovingIdx]?.focus();
+  }, [open, rovingIdx]);
 
   const current = options[currentIdx];
   if (!current) return null;
@@ -122,7 +125,7 @@ export default function ViewSwitcher<T extends string>({
                   }}
                   role="menuitemradio"
                   aria-checked={on}
-                  tabIndex={i === focusIdx ? 0 : -1}
+                  tabIndex={i === rovingIdx ? 0 : -1}
                   onClick={() => {
                     onChange(o.id);
                     close();