fix: 工具面板/帮助面板同步更新 + 图片上传限制

- 工具面板: 20→29个工具，补齐 web_search/memory_*/session_*/spawn_task/browser_*
- 帮助面板: 工具数量21→29，新增人格模式/MCP/Cron/Heartbeat说明，补充/retry等命令
- 图片上传: preload透传完整options，ipc尊重multiple参数，图片选择器限制单文件

src/renderer/components/input-area.ts

@@ -90,7 +90,9 @@ export function initInputArea(): void {
     const bridge = getBridge();
     if (!bridge) return;
     const paths = await bridge.dialog.openFile({
-      filters: [{ name: '图片', extensions: ['png', 'jpg', 'jpeg', 'gif', 'webp', 'bmp', 'svg'] }]
+      filters: [{ name: '图片', extensions: ['png', 'jpg', 'jpeg', 'gif', 'webp', 'bmp', 'svg'] }],
+      properties: ['openFile'],
+      multiple: false
     });
     if (!paths || paths.length === 0) return;
     await handleImagePaths(paths);