fix(user-input): clear mention state on submit

Programmatic plusMenuRef.close() sets the dropdown's internal open=false but
Radix doesn't fire onOpenChange for controlled changes, so handlePlusMenuClose
never ran and mentionRangeRef stayed truthy after submitting a message with
an active @mention. That caused the keydown handler to keep intercepting
ArrowUp/ArrowDown/Tab post-submit, breaking the "edit last queued message"
ArrowUp shortcut until the user typed again.

Clear mentionRangeRef and mentionQuery inline alongside the close() call.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: TheodoreSpeaks

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

@@ -470,7 +470,11 @@ export const UserInput = forwardRef<UserInputHandle, UserInputProps>(function Us
     currentFiles.clearAttachedFiles()
     prevSelectedContextsRef.current = []
     currentContext.clearContexts()
+    // Programmatic close() bypasses Radix's onOpenChange, so handlePlusMenuClose won't
+    // fire — clear mention state inline so ArrowUp etc. aren't intercepted post-submit.
     plusMenuRef.current?.close()
+    mentionRangeRef.current = null
+    setMentionQuery(null)
 
     if (textareaRef.current) {
       textareaRef.current.style.height = 'auto'