fix(ci): 用 Python 重写 pre-build 脚本，替换 PowerShell 依赖

Gitea 自建 runner 镜像不含 PowerShell，导致 Run Pre-Build Scripts
以 exitcode 127 失败。改用 Python 3（GitHub/Gitea runner 均预装），
跨平台通用，迁回 GitHub 无需改回。

.github/workflows/deploy.yml

@@ -158,8 +158,8 @@ jobs:
           ${{ runner.os }}-hugo-
 
     - name: Run Pre-Build Scripts
-      shell: pwsh
-      run: ./scripts/add_draft_to_hidden.ps1
+      shell: bash
+      run: python3 scripts/add_draft_to_hidden.py
 
     - name: Optimize Images
       continue-on-error: true