Replace munki-pkg with swiftpkg for managed Python packaging

从 build_python_framework_pkgs.zsh 开始，重点检查 build_pkg()、munki-pkg bootstrap 变量以及现有的 build-info.json 生成流程。然后检查 Python 3.11–3.14 的 workflow 文件和 README 中的前置条件。在 Apple Silicon 上比较 baseline package 和替换 package，并使用列出的 shell、签名、notarization、smoke test 和 artifact 检查来验证是否完成。

Objective

Migrate this repository's managed Python installer packaging to codecarton/swiftpkg and retire the munki-pkg build dependency.

Current behavior

build_python_framework_pkgs.zsh downloads a pinned munki-pkg commit using MP_SHA, MP_BINDIR, and MP_ZIP. Its build_pkg() function generates recommended/build-info.json, stages preinstall-cleanup, invokes munkipkg, and moves the signed package into outputs/. Notarization and stapling run separately. Without an installer identity, the script skips package creation and still produces the framework ZIP.

Implementation scope

• Select and pin a published swiftpkg CLI release compatible with Apple Silicon build hosts; verify the downloaded artifact against a pinned SHA-256 and document prerequisites.
• Replace the munki-pkg download, temporary paths, and invocation with swiftpkg; propagate failures clearly.
• Validate compatibility of every generated build-info setting, especially ownership, suppress_bundle_relocation, preserve_xattr, distribution_style, and signing_info. Implement equivalent behavior for any unsupported settings.
• Preserve the package identifier (io.macadmins.python.recommended), version derivation, output filename/location, payload layout, permissions, symlinks, extended attributes, and preinstall cleanup behavior.
• Preserve framework code signing and the existing installer signing/notarization/stapling sequence; avoid duplicate notarization.
• Ensure Python 3.11, 3.12, 3.13, and 3.14 workflows use the replacement and continue publishing expected artifacts; update workflows only where necessary.
• Update README build prerequisites and credits. Remove active munki-pkg dependencies and obsolete bootstrap references while retaining appropriate historical attribution.

Acceptance criteria

• Local and CI packaging use the pinned swiftpkg CLI with verified artifact integrity; no active build path downloads or executes munki-pkg.
• All generated build-info options have verified equivalent behavior, with any migration differences documented.
• On Apple Silicon, inspect a baseline munki-pkg package and replacement package to confirm equivalent receipts, version, install paths, payload, ownership/modes, symlinks, extended attributes, installer scripts, and non-relocation behavior.
• Signed packages pass signature checks, notarization, and stapling validation using the existing signing credentials.
• Clean-install and upgrade smoke tests on a disposable Apple Silicon Mac confirm preinstall cleanup, framework installation at /Library/ManagedFrameworks/Python/Python3.framework, the managed_python3 symlink, and execution/imports of the managed runtime and bundled dependencies.
• The no-installer-identity path continues producing the framework ZIP without requiring signing credentials.
• Each supported Python workflow builds and publishes the expected package artifact.
• zsh -n build_python_framework_pkgs.zsh passes; any modified workflow YAML parses successfully.
• README documents the replacement tool, pinned version/update procedure, and prerequisites.

Boundaries

This change replaces the package builder. It does not remove support for deploying the resulting installer through Munki, change Python/runtime dependencies, add the Swiftpkgr desktop app, or change the managed framework's installation contract.