feat: add titlebar to popout window with minimize/maximize/close buttons

- Add window-minimize, window-maximize, window-close, window-is-maximized IPC handlers
- Add titlebar with window controls to PopoutPage
- Update preload and types for new window control APIs

electron/preload.ts

@@ -54,4 +54,8 @@ contextBridge.exposeInMainWorld('electronAPI', {
   terminalGetStatus: () => ipcRenderer.invoke('terminal-get-status'),
   terminalGetPort: () => ipcRenderer.invoke('terminal-get-port'),
   createWindow: (tabData: { route: string; title: string }) => ipcRenderer.invoke('create-window', tabData),
+  windowMinimize: () => ipcRenderer.invoke('window-minimize'),
+  windowMaximize: () => ipcRenderer.invoke('window-maximize'),
+  windowClose: () => ipcRenderer.invoke('window-close'),
+  windowIsMaximized: () => ipcRenderer.invoke('window-is-maximized'),
 })