♿ disable sidebar toggle in fullscreen mode

src/renderer/App.tsx

@@ -141,12 +141,14 @@ export default function App(): JSX.Element {
               className={`app-layout-toggle-seg${sidebarOpen ? ' active' : ''}`}
               onClick={() => setSidebarOpen((v) => { const next = !v; localStorage.setItem('sidebarOpen', String(next)); return next })}
               title={sidebarOpen ? 'Hide file tree' : 'Show file tree'}
+              disabled={focusMode}
             />
             <div className="app-layout-toggle-seg app-layout-toggle-seg--mid" />
             <button
               className={`app-layout-toggle-seg${chatOpen ? ' active' : ''}`}
               onClick={() => setChatOpen((v) => { const next = !v; localStorage.setItem('chatOpen', String(next)); return next })}
               title={chatOpen ? 'Hide AI chat' : 'Show AI chat'}
+              disabled={focusMode}
             />
           </div>
           <div className="app-titlebar-icon-group">

src/renderer/styles/app.css

@@ -128,6 +128,12 @@
   border-color: var(--text-muted);
 }
 
+.app-layout-toggle-seg:disabled {
+  opacity: 0.25;
+  cursor: default;
+  pointer-events: none;
+}
+
 /* Middle segment: wider, non-interactive, always "on" */
 .app-layout-toggle-seg--mid {
   width: 22px;