feat: add Electron support for headless exe service

- Add folder selection button in UI
- Add Electron main process with IPC handlers
- Support --port and --docs command line arguments
- Support --headless mode for headless service
- Add portable exe build configuration

electron/preload.mjs

@@ -0,0 +1,9 @@
+import { contextBridge, ipcRenderer } from 'electron';
+
+contextBridge.exposeInMainWorld('electronAPI', {
+  selectFolder: () => ipcRenderer.invoke('select-folder'),
+  getDocsPath: () => ipcRenderer.invoke('get-docs-path'),
+  onDocsPathChanged: (callback: (path: string) => void) => {
+    ipcRenderer.on('docs-path-changed', (_event, path) => callback(path));
+  },
+});