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/App.jsx

@@ -92,6 +92,8 @@ export default function App() {
       { keys: `${layout.keys.shift}+${layout.keys.enter}`, desc: t('statusbar.newLine') },
     ],
     shell: [
+      { keys: `${layout.keys.ctrl}+${layout.keys.shift}+C`, desc: t('statusbar.copy') },
+      { keys: `${layout.keys.ctrl}+${layout.keys.shift}+V`, desc: t('statusbar.paste') },
       { keys: layout.keys.enter, desc: t('statusbar.runCommand') },
       { keys: `${layout.keys.up}/${layout.keys.down}`, desc: t('statusbar.commandHistory') },
     ],