feat(windows): replace php-sdk-binary-tools with MSYS2 + 7za-win

- Add msys2-build-essentials target: downloads the MSYS2 nightly sfx,
  extracts it, disables PGP keyring (CI-safe), runs two-pass pacman
  update, and installs autotools build essentials (make, autoconf,
  automake, libtool, pkgconf, perl).
- Add 7za-win target: downloads 7za.exe to PKG_ROOT_PATH\bin.
- Remove php-sdk-binary-tools target and all PHP_SDK_PATH references;
  replace with SPC_MSYS2_PATH throughout Artifact, ArtifactExtractor,
  FileSystem, DefaultShell and MSVCToolchain.
- Replace {php_sdk_path} path placeholder with {spc_msys2_path}.
- WindowsToolCheck: replace checkSDK/installSDK with checkMsys2,
  installMsys2 and check7zaWin/install7zaWin fix items.
- nasm.yml: extract nasm.exe/ndisasm.exe to {pkg_root_path}/bin.
- env.ini: rename PHP_SDK_PATH to SPC_MSYS2_PATH.
- Docs: update Windows migration guide and package-model placeholder docs.

src/Package/Artifact/msys2_build_essentials.php

@@ -0,0 +1,93 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Package\Artifact;
+
+use StaticPHP\Artifact\ArtifactDownloader;
+use StaticPHP\Artifact\Downloader\DownloadResult;
+use StaticPHP\Attribute\Artifact\AfterBinaryExtract;
+use StaticPHP\Attribute\Artifact\BinaryExtract;
+use StaticPHP\Attribute\Artifact\CustomBinary;
+use StaticPHP\Exception\DownloaderException;
+use StaticPHP\Util\FileSystem;
+use StaticPHP\Util\GlobalEnvManager;
+
+class msys2_build_essentials
+{
+    // MSYS subsystem packages required for autotools-based builds.
+    private const REQUIRED_PACKAGES = ['make', 'autoconf', 'automake', 'libtool', 'pkgconf', 'perl'];
+
+    #[CustomBinary('msys2-build-essentials', ['windows-x86_64'])]
+    public function downBinary(ArtifactDownloader $downloader): DownloadResult
+    {
+        // MSYS2 nightly self-extracting archive; running it with `-y -oTARGET` extracts to TARGET\msys64\.
+        $url = 'https://github.com/msys2/msys2-installer/releases/download/nightly-x86_64/msys2-base-x86_64-latest.sfx.exe';
+        $filename = 'msys2-base-x86_64-latest.sfx.exe';
+        $path = DOWNLOAD_PATH . DIRECTORY_SEPARATOR . $filename;
+
+        default_shell()->executeCurlDownload($url, $path, retries: $downloader->getRetry());
+
+        return DownloadResult::file(
+            $filename,
+            ['url' => $url, 'version' => 'nightly'],
+            version: 'nightly',
+            extract: '{pkg_root_path}/msys2-build-essentials',
+        );
+    }
+
+    #[BinaryExtract('msys2-build-essentials', ['windows-x86_64'])]
+    public function extractBinary(string $source_file, string $target_path): void
+    {
+        $target_path = FileSystem::convertPath($target_path);
+        $source_file = FileSystem::convertPath($source_file);
+
+        // Guard: skip re-extraction if already initialized (marker written at end of this method).
+        $marker = "{$target_path}\\.spc-msys2-initialized";
+        if (file_exists($marker)) {
+            return;
+        }
+
+        if (!is_dir($target_path)) {
+            FileSystem::createDir($target_path);
+        }
+
+        cmd()->exec("\"{$source_file}\" -y -o\"{$target_path}\"");
+
+        $msys2_bin = "{$target_path}\\msys64\\usr\\bin";
+        if (!file_exists("{$msys2_bin}\\bash.exe")) {
+            throw new DownloaderException("MSYS2 extraction failed: bash.exe not found at {$msys2_bin}\\bash.exe");
+        }
+
+        // Add MSYS2 usr\bin to PATH so pacman.exe can load msys-2.0.dll.
+        GlobalEnvManager::addPathIfNotExists($msys2_bin);
+        GlobalEnvManager::putenv('CHERE_INVOKING=yes');
+        GlobalEnvManager::putenv('MSYSTEM=MSYS');
+
+        // Disable PGP signature checking: pacman-key --init requires a pseudo-TTY which is unavailable
+        // from PHP. Patching pacman.conf is the standard approach for CI pipelines.
+        $pacman_conf = "{$target_path}\\msys64\\etc\\pacman.conf";
+        FileSystem::replaceFileRegex($pacman_conf, '/^SigLevel\s*=.*$/m', 'SigLevel = Never');
+
+        $pacman = "{$target_path}\\msys64\\usr\\bin\\pacman.exe";
+
+        // Two-pass update as recommended by MSYS2 CI docs.
+        cmd()->exec("\"{$pacman}\" --noconfirm -Syuu");
+        cmd()->exec("\"{$pacman}\" --noconfirm -Syuu");
+
+        $pkgs = implode(' ', self::REQUIRED_PACKAGES);
+        cmd()->exec("\"{$pacman}\" --noconfirm -S --needed {$pkgs}");
+
+        FileSystem::writeFile($marker, date('Y-m-d H:i:s'));
+    }
+
+    #[AfterBinaryExtract('msys2-build-essentials', ['windows-x86_64'])]
+    public function afterExtract(string $target_path): void
+    {
+        $target_path = FileSystem::convertPath($target_path);
+        $msys2_root = "{$target_path}\\msys64";
+
+        GlobalEnvManager::putenv("SPC_MSYS2_PATH={$msys2_root}");
+        GlobalEnvManager::addPathIfNotExists("{$msys2_root}\\usr\\bin");
+    }
+}