fix(download): 下载设置抽屉打开时路径显示为空

get-store-value 主进程用 ipcMain.on 同步返回，renderer 却用 invoke 读取会直接
reject，导致 initDownloadSettings 中断、已保存的下载路径等配置回读失败。改为
sendSync，与项目其它调用点保持一致。

contentLength 类型错误非本次提交引入，因无法通过 precommit 检查，故一并修复。

src/main/modules/downloadManager.ts

@@ -523,7 +523,7 @@ class DownloadManager {
       } else {
         // Full response (200) - start from beginning
         task.loaded = 0;
-        const contentLength = response.headers['content-length'];
+        const contentLength = response.headers['content-length'] as string;
         task.total = contentLength ? parseInt(contentLength, 10) : 0;
       }
 

src/renderer/views/download/DownloadPage.vue

@@ -915,16 +915,16 @@ const saveDownloadSettings = () => {
 };
 
 const initDownloadSettings = async () => {
-  const path = await window.electron.ipcRenderer.invoke('get-store-value', 'set.downloadPath');
-  const nameFormat = await window.electron.ipcRenderer.invoke(
+  const path = window.electron.ipcRenderer.sendSync('get-store-value', 'set.downloadPath');
+  const nameFormat = window.electron.ipcRenderer.sendSync(
     'get-store-value',
     'set.downloadNameFormat'
   );
-  const separator = await window.electron.ipcRenderer.invoke(
+  const separator = window.electron.ipcRenderer.sendSync(
     'get-store-value',
     'set.downloadSeparator'
   );
-  const saveLyric = await window.electron.ipcRenderer.invoke(
+  const saveLyric = window.electron.ipcRenderer.sendSync(
     'get-store-value',
     'set.downloadSaveLyric'
   );