Rename extension references from Chrome to Chromium

Updated all documentation, configuration, and code references from 'Xget for Chrome' to 'Xget for Chromium' for consistency with the supported browser family. This includes issue templates, workflow files, privacy and security policies, README, manifest, package metadata, background and content scripts, and popup UI.

.github/workflows/publish-extension.yml

@@ -172,7 +172,7 @@ jobs:
         uses: softprops/action-gh-release@v2
         with:
           tag_name: v${{ steps.version.outputs.version }}
-          name: Xget for Chrome ${{ steps.version.outputs.version }}
+          name: Xget for Chromium ${{ steps.version.outputs.version }}
           files: |
             chrome-extension.zip
             edge-extension.zip
@@ -185,7 +185,7 @@ jobs:
 
             - **Chrome 网上应用店**: [从 Chrome 网上应用店安装](https://chromewebstore.google.com/detail/ajiejgobfcifcikbahpijopolfjoodgf)
             - **Microsoft Edge 加载项**: [从 Microsoft Edge 加载项安装](https://microsoftedge.microsoft.com/addons/detail/jigpfhbegabdenhihpplcjhpfdcgnalc)
-            - **手动安装**: 下载下面的文件或查看 [安装指南](https://github.com/xixu-me/Xget-for-Chrome?tab=readme-ov-file#-%E5%AE%89%E8%A3%85) 获取详细说明
+            - **手动安装**: 下载下面的文件或查看 [安装指南](https://github.com/xixu-me/Xget for Chromium?tab=readme-ov-file#-%E5%AE%89%E8%A3%85) 获取详细说明
 
             ## 📁 可用文件
 
@@ -221,7 +221,7 @@ jobs:
 
       - name: 通知成功
         run: |
-          echo "🎉 成功发布 Xget for Chrome ${{ steps.version.outputs.version }} 到多个商店！"
+          echo "🎉 成功发布 Xget for Chromium ${{ steps.version.outputs.version }} 到多个商店！"
           echo "🔗 Chrome 网上应用店: https://chrome.google.com/webstore/detail/${{ secrets.CHROME_EXTENSION_ID }}"
           echo "🔗 Microsoft Edge 加载项: 查看发布页面获取手动安装文件"
           echo "📦 GitHub 发布: https://github.com/${{ github.repository }}/releases/tag/v${{ steps.version.outputs.version }}"