feat(phase1): architecture skeleton

- Electron 33 main process with frameless window, IPC, win-state persistence
- Preload with contextBridge typed API (window, theme, dialog)
- Vue 3 + Pinia + Element Plus + Vue Router renderer
- Dark/light dual theme via CSS custom properties
- TitleBar with window controls + theme toggle
- StatusBar placeholder
- Design spec document

src/preload/index.ts

@@ -0,0 +1,23 @@
+// src/preload/index.ts
+import { contextBridge, ipcRenderer } from 'electron'
+
+const electronAPI = {
+  window: {
+    minimize: () => ipcRenderer.send('window:minimize'),
+    maximize: () => ipcRenderer.send('window:maximize'),
+    close: () => ipcRenderer.send('window:close'),
+  },
+  theme: {
+    get: (): Promise<boolean> => ipcRenderer.invoke('theme:get'),
+    set: (theme: 'system' | 'dark' | 'light') => ipcRenderer.send('theme:set', theme),
+    onOsUpdated: (callback: (isDark: boolean) => void) => {
+      ipcRenderer.on('theme:os-updated', (_event, isDark: boolean) => callback(isDark))
+    },
+  },
+  dialog: {
+    openFile: (options: { title?: string; filters?: { name: string; extensions: string[] }[] }) =>
+      ipcRenderer.invoke('dialog:openFile', options),
+  },
+}
+
+contextBridge.exposeInMainWorld('electronAPI', electronAPI)