fix(workflows): use shell:powershell (PS 5.1) instead of pwsh; fix ciScriptsDir path

- All 3 workflows: pwsh -> powershell (host requires PS 5.1, not Core 7+)
- workflow-example.yml: replace GITHUB_WORKSPACE-relative ciScriptsDir with
  hardcoded host path; use SSH alias URL (host-clone mode) instead of HTTP
- docs: add WORKFLOW-AUTHORING.md reference for AI and developers

gitea/workflows/build-nsis.yml

@@ -25,7 +25,7 @@ jobs:
 
     steps:
       - name: Run CI Job
-        shell: pwsh
+        shell: powershell
         run: |
           & 'N:\Code\Workspace\Local-CI-CD-System\scripts\Invoke-CIJob.ps1' `
             -JobId               '${{ github.run_id }}' `