feat: update action.yml to use pwsh shell and enhance vm.py with start option; add credential management scripts

tools/ci-cred-set.py

@@ -0,0 +1,28 @@
+#!/opt/ci/venv/bin/python
+"""Store a CI credential in the file keyring for ci-runner (two-entry scheme).
+
+Usage:
+    sudo -u ci-runner /opt/ci/venv/bin/python tools/ci-cred-set.py <target> [<username>]
+
+Examples:
+    sudo -u ci-runner /opt/ci/venv/bin/python tools/ci-cred-set.py BuildVMGuest "WINBUILD-2025\\ci_build"
+    sudo -u ci-runner /opt/ci/venv/bin/python tools/ci-cred-set.py GiteaPAT ci-runner-linux
+"""
+import getpass
+import sys
+
+try:
+    import keyring
+except ImportError:
+    sys.exit("keyring not installed")
+
+target   = sys.argv[1] if len(sys.argv) > 1 else "BuildVMGuest"
+username = sys.argv[2] if len(sys.argv) > 2 else input(f"Username for {target}: ")
+password = getpass.getpass(f"Password for {target}/{username}: ")
+
+# Entry 1: password, keyed by (service=target, username=username)
+keyring.set_password(target, username, password)
+# Entry 2: username stored separately so get_credential(target, None) can find it
+keyring.set_password(f"{target}:meta", "username", username)
+
+print(f"Stored: service={target!r}  username={username!r}")