feat: TypeScript + Electron v2 重构 - 纯桌面版

- 全面迁移到 TypeScript，严格类型定义
- 放弃 Web 版，专注 Electron 桌面应用
- 主进程模块化：main.ts, preload.ts, menu.ts, tray.ts, ipc.ts, utils.ts
- 渲染进程完整迁移所有功能组件
- 删除 PWA 相关文件 (sw.js, manifest.json)
- 删除 Web 版降级逻辑
- 保留所有核心功能：流式对话、多模型、Think推理、多模态、RAG知识库、Agent预设、历史管理
- 保留 Windows 11 Fluent Design 暗色主题样式

src/renderer/components/lightbox.ts

@@ -0,0 +1,32 @@
+/**
+ * Lightbox - 图片预览组件
+ */
+
+let lightboxEl: HTMLElement, lightboxImg: HTMLImageElement;
+
+export function initLightbox(): void {
+  lightboxEl = document.querySelector('#lightbox')!;
+  lightboxImg = document.querySelector('#lightboxImg')!;
+
+  lightboxEl.addEventListener('click', (e) => {
+    if (e.target === lightboxEl) closeLightbox();
+  });
+  document.querySelector('#lightboxClose')!.addEventListener('click', closeLightbox);
+
+  document.querySelector('#messagesContainer')?.addEventListener('click', (e) => {
+    const target = e.target as HTMLElement;
+    if ((target as HTMLImageElement).dataset.lightbox === 'true') {
+      openLightbox((target as HTMLImageElement).src);
+    }
+  });
+}
+
+export function openLightbox(src: string): void {
+  lightboxImg.src = src;
+  lightboxEl.style.display = '';
+}
+
+export function closeLightbox(): void {
+  lightboxEl.style.display = 'none';
+  lightboxImg.src = '';
+}