feat(ui): add collapsible persistent sidebar

src/components/settings/SettingsView.tsx

@@ -216,6 +216,23 @@ export default function SettingsView() {
                   <span className="w-12 text-right text-xs tabular-nums text-txt-muted">{settings.sidebarWidth}px</span>
                 </div>
               </SettingRow>
+              <SettingRow label="折叠侧栏" description="隐藏会话树以专心操作终端，可用 Ctrl/Cmd+B 切换">
+                <button
+                  type="button"
+                  role="switch"
+                  aria-checked={settings.sidebarCollapsed}
+                  onClick={() => setSetting('sidebarCollapsed', !settings.sidebarCollapsed)}
+                  className={`relative h-6 w-11 rounded-full transition-colors ${
+                    settings.sidebarCollapsed ? 'bg-accent-blue' : 'bg-dark-600'
+                  }`}
+                >
+                  <span
+                    className={`absolute top-0.5 left-0.5 h-5 w-5 rounded-full bg-white transition-transform ${
+                      settings.sidebarCollapsed ? 'translate-x-5' : 'translate-x-0'
+                    }`}
+                  />
+                </button>
+              </SettingRow>
             </SettingGroup>
           </div>
         )