Versions-Definition: --version mit Remote-Check + README-Mismatch-Warnung

- Program.cs: PrintVersion() vergleicht Assembly-Version mit README.md
  (Block-Quote '> **Version: X.Y.Z**') und warnt bei Mismatch.
  Remote-Check via 'git ls-remote origin HEAD' vergleicht lokalen mit
  remote Commit-Hash; Hinweis 'UPDATE AVAILABLE' bei Differenz.
  Copy-Installationen (kein .git) erhalten Hinweis auf ./install.sh.
- README.md: Versions-Block-Quote unter dem Titel (kanonisch),
  Update-Check-Doku, drei synchrone Versionsquellen dokumentiert.
- AGENTS.md: Versions-Definition als Definition of Done für Releases
  (README + csproj + Assembly müssen synchron sein).

src/Program.cs

@@ -24,10 +24,7 @@ if (argsList.Contains("--help") || argsList.Contains("-h") || argsList.Contains(
 }
 if (argsList.Contains("--version"))
 {
-    var v = System.Reflection.Assembly.GetExecutingAssembly().GetName().Version;
-    Console.WriteLine($"GCBoK.WebStaticBuilder {v?.ToString() ?? "0.0.0"}");
-    var hash = GitShortHash(AppContext.BaseDirectory);
-    if (hash != null) Console.WriteLine($"commit: {hash}");
+    PrintVersion(verbose);
     return;
 }
 
@@ -411,3 +408,115 @@ static void ShowStatus(string rootDir)
     var markdown = File.ReadAllText(readme);
     MarkdownConsoleRenderer.Render(markdown, Console.Out);
 }
+
+static void PrintVersion(bool verbose)
+{
+    var v = System.Reflection.Assembly.GetExecutingAssembly().GetName().Version;
+    var asmVersion = v?.ToString() ?? "0.0.0";
+    Console.WriteLine($"GCBoK.WebStaticBuilder {asmVersion}");
+
+    // README.md version check — canonical source is the block-quote
+    // "> **Version: X.Y.Z**" directly under the title.
+    var readmeVersion = ExtractReadmeVersion(AppContext.BaseDirectory);
+    if (readmeVersion != null)
+    {
+        // Assembly versions are 4-part (1.0.0.0); README uses 3-part (1.0.0).
+        // Compare the first 3 components to avoid trailing-zero noise.
+        var asmShort = v?.ToString(3) ?? asmVersion;
+        if (!string.Equals(asmShort, readmeVersion, StringComparison.OrdinalIgnoreCase))
+        {
+            Console.WriteLine($"WARNING: version mismatch — README.md says {readmeVersion}, assembly says {asmShort}");
+            Console.WriteLine("         Update README.md and/or <Version> in the .csproj to keep them in sync.");
+        }
+    }
+
+    var repo = FindRepoRoot(AppContext.BaseDirectory);
+    if (repo == null)
+    {
+        Console.WriteLine("install: copy (no git repo — version check skipped)");
+        Console.WriteLine("update:  run ./install.sh again to update");
+        return;
+    }
+
+    var localHash = GitShortHash(AppContext.BaseDirectory);
+    if (localHash != null) Console.WriteLine($"commit:  {localHash} (local)");
+
+    // Remote check (best-effort, non-blocking on failure)
+    var remoteShort = CaptureRemoteHeadShort(repo);
+    if (remoteShort == null)
+    {
+        if (verbose) Console.WriteLine("(remote check failed — no network or no upstream)");
+        return;
+    }
+
+    Console.WriteLine($"remote:  {remoteShort}");
+
+    if (localHash != null && !string.Equals(localHash, remoteShort, StringComparison.OrdinalIgnoreCase))
+    {
+        Console.WriteLine();
+        Console.WriteLine("  UPDATE AVAILABLE");
+        Console.WriteLine("  Run: webstatic update");
+    }
+    else if (localHash != null)
+    {
+        Console.WriteLine("  up to date");
+    }
+}
+
+static string? ExtractReadmeVersion(string baseDir)
+{
+    // Search upwards for README.md (it lives at the repo root, not in bin/).
+    var dir = new DirectoryInfo(Path.GetFullPath(baseDir));
+    string? readmePath = null;
+    while (dir != null)
+    {
+        var candidate = Path.Combine(dir.FullName, "README.md");
+        if (File.Exists(candidate)) { readmePath = candidate; break; }
+        dir = dir.Parent;
+    }
+    if (readmePath == null) return null;
+
+    try
+    {
+        var lines = File.ReadAllLines(readmePath);
+        // Look for "> **Version: X.Y.Z**" within the first 10 lines
+        foreach (var line in lines.Take(10))
+        {
+            var m = System.Text.RegularExpressions.Regex.Match(
+                line, @"\*\*Version:\s*(\d+\.\d+(?:\.\d+)?)\*\*",
+                System.Text.RegularExpressions.RegexOptions.IgnoreCase);
+            if (m.Success) return m.Groups[1].Value;
+        }
+    }
+    catch { /* best-effort */ }
+    return null;
+}
+
+static string? CaptureRemoteHeadShort(string repoDir)
+{
+    try
+    {
+        var psi = new ProcessStartInfo
+        {
+            FileName = "git",
+            Arguments = "ls-remote origin HEAD",
+            WorkingDirectory = repoDir,
+            RedirectStandardOutput = true,
+            RedirectStandardError = true,
+            UseShellExecute = false,
+            CreateNoWindow = true,
+        };
+        using var p = Process.Start(psi);
+        if (p == null) return null;
+        var outp = p.StandardOutput.ReadToEnd().Trim();
+        p.WaitForExit(5000); // 5s timeout
+        if (p.ExitCode != 0 || string.IsNullOrEmpty(outp)) return null;
+        // Format: "<full-sha>\tHEAD"
+        var parts = outp.Split('\t', ' ');
+        return parts.Length > 0 && parts[0].Length >= 7 ? parts[0][..7] : null;
+    }
+    catch
+    {
+        return null;
+    }
+}