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/Dashboard.jsx

@@ -93,13 +93,14 @@ export default function Dashboard({ api, refreshRef }) {
   const minimax = (quota || []).find(p => p.name === 'minimax')
   const zai = (quota || []).find(p => p.name === 'zai')
 
-  const EXCLUDE_CMDS = ['ls', 'cd', 'pwd', 'clear', 'exit', 'history']
+  const EXCLUDE_CMDS = ['ls', 'cd', 'pwd', 'clear', 'exit', 'history', 'cat', 'echo', 'grep', 'export', 'alias', 'unalias', 'set', 'unset', 'source', '.', 'fg', 'bg', 'jobs', 'wait', 'true', 'false', 'yes', 'sleep', 'date', 'whoami', 'id', 'uname', 'hostname', 'uptime', 'df', 'free', 'top', 'htop', 'nano', 'vi', 'vim', 'less', 'more', 'tail', 'head', 'man', 'info', 'which', 'whereis', 'type', 'command', 'hash', 'builtin', 'help']
 
   const topCmds = (() => {
     const counts = {}
     for (const c of recentCmds) {
       const base = c.cmd.split(/\s+/)[0]
-      if (EXCLUDE_CMDS.includes(base) || !base) continue
+      if (!base || base.length < 2 || EXCLUDE_CMDS.includes(base)) continue
+      if (!/^[a-zA-Z@.\/]/.test(base)) continue
       counts[base] = (counts[base] || 0) + 1
     }
     return Object.entries(counts)