fix(user-input): always update prevDefaultValueRef on defaultValue change

Prevents stale ref when defaultValue transitions through empty — if
defaultValue goes non-empty → empty → same non-empty value, the ref
was not updated on the empty transition, causing setValue to be skipped
on the subsequent change.

Also removes unnecessary useCallback wrapping from handleSendQueuedHead,
handleEditQueued, handleEditQueuedTail in MothershipChat — none have a
reference observer (UserInput stores them via refs, QueuedMessages is
not React.memo-wrapped).

Author: waleedlatif1

apps/sim/app/workspace/[workspaceId]/home/components/user-input/user-input.tsx

@@ -152,10 +152,9 @@ export const UserInput = forwardRef<UserInputHandle, UserInputProps>(function Us
 
   const prevDefaultValueRef = useRef(defaultValue)
   useEffect(() => {
-    if (!defaultValue) return
     if (defaultValue === prevDefaultValueRef.current) return
     prevDefaultValueRef.current = defaultValue
-    setValue(defaultValue)
+    if (defaultValue) setValue(defaultValue)
   }, [defaultValue])
 
   const files = useFileAttachments({