fix: AI terminal init, Shift+Tab nav, code block rendering, command filtering

- Fix AI terminal not initializing (wait for shell col visibility, remove offsetHeight guard)
- Add Shift+Tab to cycle between shell terminals
- Handle unclosed code blocks in renderContent (Shell + Studio)
- Filter irrelevant commands from history (short/non-alpha backend + expanded frontend exclude list)

💘 Generated with Crush

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

web/src/components/Shell.jsx

@@ -28,7 +28,16 @@ function renderContent(text) {
     lastIndex = match.index + full.length
   }
   if (lastIndex < text.length) {
-    parts.push({ type: 'text', content: text.slice(lastIndex) })
+    const remaining = text.slice(lastIndex)
+    const openBlock = remaining.match(/```(\w*)\n?([\s\S]*)$/)
+    if (openBlock) {
+      if (openBlock.index > 0) {
+        parts.push({ type: 'text', content: remaining.slice(0, openBlock.index) })
+      }
+      parts.push({ type: 'code', lang: openBlock[1] || '', content: openBlock[2] || '' })
+    } else {
+      parts.push({ type: 'text', content: remaining })
+    }
   }
   return parts
 }
@@ -308,7 +317,7 @@ export default function Shell({ api }) {
     if (tabsRef.current[tabId]) return
 
     const container = document.getElementById(`terminal-${tabId}`)
-    if (!container || container.offsetHeight === 0) return
+    if (!container) return
 
     const s = settingsRef.current
     const { term, fitAddon } = createTerminal(container, {
@@ -368,7 +377,12 @@ export default function Shell({ api }) {
     if (!tab) return
 
     const tryInit = (attempt) => {
-      if (attempt > 10) return
+      if (attempt > 20) return
+      const shellCol = document.querySelector('.shell-terminal-col')
+      if (!shellCol || shellCol.offsetParent === null) {
+        setTimeout(() => tryInit(attempt + 1), 150)
+        return
+      }
       const container = document.getElementById(`terminal-${tab.id}`)
       if (!container || container.offsetHeight === 0) {
         setTimeout(() => tryInit(attempt + 1), 100)
@@ -404,7 +418,17 @@ export default function Shell({ api }) {
   useEffect(() => {
     const onKey = (e) => {
       if (e.target.tagName === 'INPUT' || e.target.tagName === 'TEXTAREA') return
-      if (!e.altKey) return
+      if (!e.altKey && !(e.key === 'Tab' && e.shiftKey)) return
+
+      if (e.key === 'Tab' && e.shiftKey) {
+        const shellTab = document.querySelector('.shell-layout')
+        if (!shellTab || shellTab.closest('.tab-hidden')) return
+        e.preventDefault()
+        const idx = tabs.findIndex(t => t.id === activeTab)
+        const next = (idx + 1) % tabs.length
+        setActiveTab(tabs[next].id)
+        return
+      }
 
       const num = parseInt(e.key)
       if (num >= 1 && num <= tabs.length) {