Add a way to run Python scripts with the interpreter which runs Ansible

bin/ansible-python.sh runs Python with the interpreter named in the
first line of `ansible-playbook`. That interpreter has PyYAML, since
Ansible depends on it, even when Ansible is installed in an environment
of its own (e.g. with pipx), where the system's `python3` may lack it.
If it is not a Python interpreter (e.g. `ansible-playbook` is a wrapper
script), or Ansible is missing, `python3` is used.

Role installation, which needs PyYAML, is the first to use it in the
next commit, so that it works without installing PyYAML separately.

The same script in mash-playbook (where its tests live):
https://github.com/mother-of-all-self-hosting/mash-playbook/commit/1fe0f90f

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

bin/ansible-python.sh

@@ -0,0 +1,44 @@
+#!/bin/sh
+# SPDX-FileCopyrightText: 2026 MASH project contributors
+# SPDX-FileCopyrightText: 2026 Slavi Pantaleev
+#
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+# Runs Python (with the given arguments) using the interpreter which runs Ansible.
+#
+# The playbook's Python scripts need PyYAML, which Ansible depends on. The interpreter which runs Ansible
+# therefore has it, even when Ansible is installed in an environment of its own (e.g. with pipx),
+# where the system's `python3` may lack it.
+#
+# The interpreter is taken from the first line (shebang) of `ansible-playbook`.
+# If that is not a Python interpreter (e.g. `ansible-playbook` is a wrapper script), or Ansible is not installed,
+# `python3` is used.
+
+set -eu
+
+python=python3
+
+ansible_playbook_path=$(command -v ansible-playbook 2>/dev/null || true)
+if [ -n "$ansible_playbook_path" ] && [ -f "$ansible_playbook_path" ]; then
+    shebang=$(head -n 1 "$ansible_playbook_path")
+    case "$shebang" in
+        "#!"*)
+            read -r interpreter next_word _ <<EOF
+${shebang#"#!"}
+EOF
+            # `#!/usr/bin/env python3` names the interpreter in the next word
+            if [ "$(basename "$interpreter")" = "env" ]; then
+                interpreter=${next_word:-}
+            fi
+            case "$(basename "${interpreter:-none}")" in
+                python*)
+                    if command -v "$interpreter" >/dev/null 2>&1; then
+                        python=$interpreter
+                    fi
+                    ;;
+            esac
+            ;;
+    esac
+fi
+
+exec "$python" "$@"