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

runner/config.yaml

@@ -29,6 +29,10 @@ runner:
     # Snapshot to clone from. Default BaseClean — set to BaseClean_<yyyyMMdd> when
     # refreshing the template. Keep the previous value live for 1 week before deleting.
     # GITEA_CI_SNAPSHOT_NAME: "BaseClean"
+    # Path to the Linux (Ubuntu 24.04) template VM
+    GITEA_CI_LINUX_TEMPLATE_PATH: "F:\\CI\\Templates\\LinuxBuild2404\\LinuxBuild2404.vmx"
+    # SSH private key for Linux guest authentication
+    GITEA_CI_SSH_KEY_PATH: "F:\\CI\\keys\\ci_linux"
 
   # Optional: load additional env vars from a file (one KEY=VALUE per line)
   # env_file: "F:\\CI\\runner.env"
@@ -43,6 +47,7 @@ runner:
     - "windows-build:host"
     - "dotnet:host"
     - "msbuild:host"
+    - "linux-build:host"
 
   # Uncomment to ignore specific errors
   # insecure: false