refactor: migrate PDF export to desktop runtime abstraction

- Extract desktop-specific logic into src/services/desktop.ts
- Add runtime detection for Electron vs Tauri environments
- Simplify NoteEditor by delegating PDF export to desktop service
- Update printExport.ts to remove unused storage helpers
- Add Electron main process files in electron/ directory
- Update vite config and types for Electron integration
- Update .gitignore and package.json for Electron workflow

electron/main.cjs

@@ -0,0 +1,159 @@
+const fs = require('node:fs/promises');
+const path = require('node:path');
+const { app, BrowserWindow, dialog, ipcMain } = require('electron');
+
+const rendererUrl = process.env.ELECTRON_RENDERER_URL;
+const isDev = Boolean(rendererUrl);
+let mainWindow = null;
+
+const waitForPrintDocument = () => `
+  new Promise((resolve) => {
+    const pendingImages = Array.from(document.images).filter((image) => !image.complete);
+    const waitForImages = Promise.all(
+      pendingImages.map(
+        (image) =>
+          new Promise((done) => {
+            image.addEventListener('load', () => done(), { once: true });
+            image.addEventListener('error', () => done(), { once: true });
+          })
+      )
+    );
+    const waitForFonts = document.fonts ? document.fonts.ready.catch(() => undefined) : Promise.resolve();
+
+    Promise.all([waitForImages, waitForFonts]).then(() => {
+      requestAnimationFrame(() => requestAnimationFrame(() => resolve()));
+    });
+  });
+`;
+
+function createMainWindow() {
+  mainWindow = new BrowserWindow({
+    width: 1300,
+    height: 800,
+    minWidth: 800,
+    minHeight: 600,
+    show: false,
+    webPreferences: {
+      preload: path.join(__dirname, 'preload.cjs'),
+      contextIsolation: true,
+      nodeIntegration: false,
+      sandbox: false,
+    },
+  });
+
+  mainWindow.once('ready-to-show', () => {
+    mainWindow.show();
+  });
+
+  if (isDev) {
+    void mainWindow.loadURL(rendererUrl);
+    mainWindow.webContents.openDevTools({ mode: 'detach' });
+  } else {
+    void mainWindow.loadFile(path.join(__dirname, '..', 'dist', 'index.html'));
+  }
+}
+
+app.whenReady().then(() => {
+  createMainWindow();
+
+  app.on('activate', () => {
+    if (BrowserWindow.getAllWindows().length === 0) {
+      createMainWindow();
+    }
+  });
+});
+
+app.on('window-all-closed', () => {
+  if (process.platform !== 'darwin') {
+    app.quit();
+  }
+});
+
+ipcMain.handle('desktop:show-message', async (event, options) => {
+  const ownerWindow = BrowserWindow.fromWebContents(event.sender) ?? mainWindow;
+  const typeMap = {
+    info: 'info',
+    warning: 'warning',
+    error: 'error',
+  };
+
+  await dialog.showMessageBox(ownerWindow, {
+    type: typeMap[options.kind] || 'info',
+    title: options.title || app.name,
+    message: options.message,
+    buttons: ['OK'],
+    defaultId: 0,
+  });
+});
+
+ipcMain.handle('desktop:http-request', async (_event, payload) => {
+  const body =
+    payload.bodyBase64 != null
+      ? Buffer.from(payload.bodyBase64, 'base64')
+      : payload.bodyText;
+
+  const response = await fetch(payload.url, {
+    method: payload.method || 'GET',
+    headers: payload.headers,
+    body,
+  });
+
+  const buffer = Buffer.from(await response.arrayBuffer());
+
+  return {
+    ok: response.ok,
+    status: response.status,
+    statusText: response.statusText,
+    headers: Object.fromEntries(response.headers.entries()),
+    bodyBase64: buffer.toString('base64'),
+  };
+});
+
+ipcMain.handle('desktop:export-pdf', async (event, payload) => {
+  const ownerWindow = BrowserWindow.fromWebContents(event.sender) ?? mainWindow;
+  const saveResult = await dialog.showSaveDialog(ownerWindow, {
+    title: 'Export PDF',
+    defaultPath: payload.fileName,
+    filters: [{ name: 'PDF Document', extensions: ['pdf'] }],
+  });
+
+  if (saveResult.canceled || !saveResult.filePath) {
+    return { canceled: true };
+  }
+
+  const pdfWindow = new BrowserWindow({
+    width: 960,
+    height: 1100,
+    show: false,
+    parent: ownerWindow ?? undefined,
+    webPreferences: {
+      sandbox: false,
+      contextIsolation: true,
+      nodeIntegration: false,
+      spellcheck: false,
+    },
+  });
+
+  try {
+    await pdfWindow.loadURL(
+      `data:text/html;charset=utf-8,${encodeURIComponent(payload.documentHtml)}`
+    );
+    await pdfWindow.webContents.executeJavaScript(waitForPrintDocument(), true);
+
+    const pdfData = await pdfWindow.webContents.printToPDF({
+      printBackground: true,
+      preferCSSPageSize: true,
+    });
+
+    await fs.writeFile(saveResult.filePath, pdfData);
+
+    return {
+      canceled: false,
+      filePath: saveResult.filePath,
+    };
+  } finally {
+    if (!pdfWindow.isDestroyed()) {
+      pdfWindow.destroy();
+    }
+  }
+});