feat(studio): Tab focuses textarea, autocomplete commands

- Tab outside textarea focuses it
- Tab inside textarea autocompletes / commands (/clear, /summarize, etc.)

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

web/src/components/Studio.jsx

@@ -329,6 +329,20 @@ export default function Studio({ api }) {
     messagesEnd.current?.scrollIntoView({ behavior: 'smooth' })
   }, [messages, streaming, streamThinking, streamToolCalls])
 
+  useEffect(() => {
+    const onTab = (e) => {
+      if (e.key !== 'Tab') return
+      if (document.activeElement?.tagName === 'INPUT' || document.activeElement?.tagName === 'TEXTAREA') return
+      const feed = document.querySelector('.studio-feed-layout')
+      if (!feed?.closest('.tab-hidden')) {
+        e.preventDefault()
+        textareaRef.current?.focus()
+      }
+    }
+    window.addEventListener('keydown', onTab)
+    return () => window.removeEventListener('keydown', onTab)
+  }, [])
+
   useEffect(() => {
     if (textareaRef.current) {
       textareaRef.current.style.height = 'auto'
@@ -537,10 +551,38 @@ export default function Studio({ api }) {
     }
   }, [])
 
+  const COMMANDS = ['/clear', '/summarize', '/help', '/plan', '/export', '/model']
+
   const handleKeyDown = (e) => {
     if (e.key === 'Enter' && !e.shiftKey) {
       e.preventDefault()
       handleSend()
+      return
+    }
+    if (e.key === 'Tab') {
+      e.preventDefault()
+      const ta = textareaRef.current
+      if (!ta) return
+      if (document.activeElement !== ta) {
+        ta.focus()
+        return
+      }
+      const val = ta.value
+      const pos = ta.selectionStart
+      const before = val.slice(0, pos)
+      const afterSlash = before.match(/\/(\w*)$/)
+      if (afterSlash) {
+        const partial = afterSlash[0]
+        const matches = COMMANDS.filter(c => c.startsWith(partial) && c !== partial)
+        if (matches.length === 1) {
+          const completed = matches[0] + ' '
+          const newText = val.slice(0, pos - afterSlash[0].length) + completed + val.slice(pos)
+          setInput(newText)
+          requestAnimationFrame(() => {
+            ta.selectionStart = ta.selectionEnd = pos - afterSlash[0].length + completed.length
+          })
+        }
+      }
     }
   }