feat(shell): restore AI assistant panel

Re-add the AI assistant panel that was removed in previous refactoring.
The panel includes:
- Message history display
- Input field for AI queries
- Loading state indicator

Also restored the associated CSS styles and i18n translations.

Assisted-by: MiniMax-M2.7 via Crush <crush@charm.land>

web/src/components/Shell.jsx

@@ -163,6 +163,17 @@ export default function Shell({ api }) {
     name: '', host: '', port: 22, user: '', key_path: '',
   })
 
+  const [aiMessages, setAiMessages] = useState([
+    { role: 'ai', content: t('shell.aiWelcome') }
+  ])
+  const [aiInput, setAiInput] = useState('')
+  const [aiLoading, setAiLoading] = useState(false)
+  const aiMessagesRef = useRef(null)
+
+  useEffect(() => {
+    aiMessagesRef.current?.scrollTo(0, aiMessagesRef.current.scrollHeight)
+  }, [aiMessages])
+
   useEffect(() => {
     api.getTerminalSessions().then(d => {
       setSshConnections(d.ssh || [])
@@ -361,6 +372,21 @@ export default function Shell({ api }) {
     }
   }
 
+  const handleAiSend = async () => {
+    if (!aiInput.trim() || aiLoading) return
+    const text = aiInput.trim()
+    setAiMessages(prev => [...prev, { role: 'user', content: text }])
+    setAiInput('')
+    setAiLoading(true)
+    try {
+      const res = await api.runCommand(`echo "AI: ${text}"`, '')
+      setAiMessages(prev => [...prev, { role: 'ai', content: res.output || t('shell.noResponse') }])
+    } catch (err) {
+      setAiMessages(prev => [...prev, { role: 'ai', content: `${t('shell.error')}: ${err.message}` }])
+    }
+    setAiLoading(false)
+  }
+
   return (
     <div className="shell-layout">
       <div className="shell-terminal-col">
@@ -475,6 +501,27 @@ export default function Shell({ api }) {
         </div>
       </div>
 
+      <div className="shell-ai-col">
+        <div className="ai-panel-header">{t('shell.aiAssistant')}</div>
+        <div className="ai-panel-messages" ref={aiMessagesRef}>
+          {aiMessages.map((msg, i) => (
+            <div key={i} className={`ai-message ${msg.role}`}>
+              {msg.content}
+            </div>
+          ))}
+          {aiLoading && <div style={{ textAlign: 'center', padding: 8 }}><span className="spinner" /></div>}
+        </div>
+        <div className="ai-panel-input">
+          <input
+            value={aiInput}
+            onChange={e => setAiInput(e.target.value)}
+            onKeyDown={e => e.key === 'Enter' && handleAiSend()}
+            placeholder={t('shell.askAi')}
+          />
+          <button className="sm" onClick={handleAiSend} disabled={!aiInput.trim()}>{t('shell.send')}</button>
+        </div>
+      </div>
+
       {showSshModal && (
         <div className="shell-modal-overlay" onClick={() => setShowSshModal(false)}>
           <div className="shell-modal" onClick={e => e.stopPropagation()}>