fix(shell): prevent Enter in AI chat from leaking to terminal

Stop propagation of Enter keydown in AI input and defer terminal
focus to next event loop tick to prevent xterm from capturing the
same key event.

💘 Generated with Crush

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

web/src/components/Shell.jsx

@@ -693,7 +693,7 @@ export default function Shell({ api }) {
 
     if (!fromEvent) {
       setAiInput('')
-      focusAiTerminal()
+      setTimeout(() => focusAiTerminal(), 0)
     }
 
     if (trimmed === '/clear') {
@@ -937,7 +937,7 @@ export default function Shell({ api }) {
           <input
             value={aiInput}
             onChange={e => setAiInput(e.target.value)}
-            onKeyDown={e => e.key === 'Enter' && handleAiSend()}
+            onKeyDown={e => { if (e.key === 'Enter') { e.preventDefault(); e.stopPropagation(); handleAiSend() } }}
             placeholder={aiAtLimit ? '/clear pour continuer' : t('shell.askAi')}
             disabled={aiAtLimit && aiInput !== '/clear'}
           />