Address code review: extract disabled logic, document tool role in docs

Agent-Logs-Url: https://github.com/objectstack-ai/objectui/sessions/40e1c13a-9cc3-482e-9ab3-f43e05a917c3

Co-authored-by: xuyushun441-sys <255036401+xuyushun441-sys@users.noreply.github.com>

Author: Copilot

content/docs/plugins/plugin-chatbot.mdx

@@ -300,6 +300,27 @@ System messages appear centered with muted styling:
 }
 ```
 
+### Tool Messages (AI Mode)
+
+Tool messages represent results from tool invocations during AI streaming. They are generated automatically by the vercel/ai SDK when the backend performs tool calls (e.g., fetching weather, querying a database). Tool messages are not displayed directly — their results are embedded in the assistant message's `toolInvocations` array:
+
+```tsx
+{
+  id: '4',
+  role: 'assistant',
+  content: 'The weather in SF is 68°F.',
+  toolInvocations: [
+    {
+      toolCallId: 'tc-1',
+      toolName: 'getWeather',
+      args: { city: 'San Francisco' },
+      result: { temp: 68, condition: 'Sunny' },
+      state: 'result',
+    }
+  ]
+}
+```
+
 ## Examples
 
 ### Simple AI Chat

packages/plugin-chatbot/src/ChatbotEnhanced.tsx

@@ -167,6 +167,9 @@ const ChatbotEnhanced = React.forwardRef<HTMLDivElement, ChatbotEnhancedProps>(
       }
     }
 
+    const isInputDisabled = disabled || isLoading
+    const isSendDisabled = isInputDisabled || (!inputValue.trim() && selectedFiles.length === 0)
+
     const handleKeyDown = (e: React.KeyboardEvent<HTMLInputElement>) => {
       if (e.key === "Enter" && !e.shiftKey) {
         e.preventDefault()
@@ -386,7 +389,7 @@ const ChatbotEnhanced = React.forwardRef<HTMLDivElement, ChatbotEnhancedProps>(
                 variant="ghost"
                 size="icon"
                 onClick={() => fileInputRef.current?.click()}
-                disabled={disabled || isLoading}
+                disabled={isInputDisabled}
                 aria-label="Attach file"
               >
                 <Paperclip className="h-4 w-4" />
@@ -400,13 +403,13 @@ const ChatbotEnhanced = React.forwardRef<HTMLDivElement, ChatbotEnhancedProps>(
             onChange={(e) => setInputValue(e.target.value)}
             onKeyDown={handleKeyDown}
             placeholder={placeholder}
-            disabled={disabled || isLoading}
+            disabled={isInputDisabled}
             className="flex-1"
           />
 
           <Button
             onClick={handleSend}
-            disabled={disabled || isLoading || (!inputValue.trim() && selectedFiles.length === 0)}
+            disabled={isSendDisabled}
             size="icon"
             aria-label="Send message"
           >