chore: update runner config and workflow example for linux-build label

runner/config.yaml:
- Add linux-build:host label alongside windows-build:host
- capacity remains 4 (concurrent jobs)

gitea/workflow-example.yml:
- Add linux-build job example (runs-on: linux-build:host)
- Document GuestOS auto-detection and SSH transport parameters

gitea/workflow-example.yml

@@ -117,3 +117,52 @@ jobs:
 #             -Branch        "${{ github.ref_name }}" `
 #             -Configuration "${{ matrix.config }}" `
 #             -VMIPAddress   "${{ matrix.vm_ip }}"
+
+---
+# CROSS-PLATFORM MATRIX BUILD (Windows + Linux VMs)
+# Runs the same build on both Windows and Linux ephemeral VMs in parallel.
+# Requires:
+#   - runner/config.yaml labels include "windows-build:host" and "linux-build:host"
+#   - Linux template provisioned: F:\CI\Templates\LinuxBuild2404\LinuxBuild2404.vmx
+#   - SSH key at F:\CI\keys\ci_linux (ed25519, no passphrase), user ci_build
+#
+# jobs:
+#   build:
+#     strategy:
+#       matrix:
+#         target: [windows, linux]
+#       fail-fast: false
+#
+#     runs-on: ${{ matrix.target }}-build
+#
+#     steps:
+#       - uses: actions/checkout@v4
+#
+#       - name: Build on ${{ matrix.target }}
+#         shell: pwsh
+#         run: |
+#           $ErrorActionPreference = 'Stop'
+#           $ciScriptsDir = Join-Path $env:GITHUB_WORKSPACE 'scripts'
+#
+#           $templatePath = if ('${{ matrix.target }}' -eq 'linux') {
+#             $env:GITEA_CI_LINUX_TEMPLATE_PATH    # F:\CI\Templates\LinuxBuild2404\LinuxBuild2404.vmx
+#           } else {
+#             $env:GITEA_CI_TEMPLATE_PATH          # F:\CI\Templates\WinBuild2025\WinBuild2025.vmx
+#           }
+#
+#           & "$ciScriptsDir\Invoke-CIJob.ps1" `
+#             -JobId        "${{ github.run_id }}-${{ github.run_attempt }}-${{ matrix.target }}" `
+#             -RepoUrl      "${{ github.server_url }}/${{ github.repository }}.git" `
+#             -Branch       "${{ github.ref_name }}" `
+#             -Commit       "${{ github.sha }}" `
+#             -TemplatePath $templatePath `
+#             -BuildCommand 'make all'
+#
+#       - name: Upload artifacts (${{ matrix.target }})
+#         if: success()
+#         uses: actions/upload-artifact@v4
+#         with:
+#           name: build-${{ matrix.target }}-${{ github.sha }}
+#           path: F:\CI\Artifacts\${{ github.run_id }}-${{ github.run_attempt }}-${{ matrix.target }}\
+#           retention-days: 14
+#           if-no-files-found: error