feat(terminal): add Ctrl+Shift+C/V copy/paste shortcuts

xterm captures all keyboard input which prevents standard clipboard
operations. Add custom key handler to intercept Ctrl+Shift+C for
copy (selection) and Ctrl+Shift+V for paste, without interfering
with Ctrl+C (SIGINT) or browser devtools shortcut.

💘 Generated with Crush

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

web/src/components/Shell.jsx

@@ -143,6 +143,32 @@ function createTerminal(container, settings = {}) {
   const webLinksAddon = new WebLinksAddon()
   term.loadAddon(fitAddon)
   term.loadAddon(webLinksAddon)
+
+  term.attachCustomKeyEventHandler((e) => {
+    if (e.type !== 'keydown') return true
+    const ctrl = e.ctrlKey || e.metaKey
+    const shift = e.shiftKey
+
+    if (ctrl && shift && e.key === 'C') {
+      e.preventDefault()
+      e.stopPropagation()
+      const selection = term.getSelection()
+      if (selection) navigator.clipboard.writeText(selection)
+      return false
+    }
+
+    if (ctrl && shift && e.key === 'V') {
+      e.preventDefault()
+      e.stopPropagation()
+      navigator.clipboard.readText().then(text => {
+        if (text) term.paste(text)
+      }).catch(() => {})
+      return false
+    }
+
+    return true
+  })
+
   term.open(container)
   fitAddon.fit()