Server updates from the web panel with progress screen

- Updater checks git.mbm.wtf every 6 h (and on demand) for a newer <Version>
  on main, shows the new commits and the required mod version
- Install: download the source, build it with dotnet publish into
  data/app/current, warn players and restart (exit code 75 for Docker/systemd,
  self-relaunch on Windows). At startup a newer installed update is loaded in
  its own AssemblyLoadContext; after 3 failed starts the built-in version runs
- Panel: Update page, sidebar badge, full-screen progress overlay (download,
  build, install, restart) that survives the restart and reloads the panel
- Panel sessions survive restarts (hashed tokens in data/panel_sessions.json)
- Docker image is based on the .NET SDK so it can build updates
- Version 2.9.0

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Program.cs

@@ -6,6 +6,8 @@ using MSCO.Server;
 string dataDir = ArgValue("--data") ?? Environment.GetEnvironmentVariable("MSCO_DATA") ?? AppContext.BaseDirectory;
 dataDir = Path.GetFullPath(dataDir);
 Directory.CreateDirectory(dataDir);
+// Im Panel installiertes, neueres Update (DATA/app/current)? Dann läuft stattdessen das.
+if (Array.IndexOf(args, "--cmd") < 0 && Updater.RunInstalled(args, dataDir) is int updatedExit) return updatedExit;
 string configPath = Path.Combine(dataDir, "server.json");
 string commandFile = Path.Combine(dataDir, "commands.in");
 
@@ -22,7 +24,7 @@ if (Array.IndexOf(args, "--cmd") >= 0)
 }
 
 try { Console.Title = "MSCO Server"; } catch { } // nicht jedes Terminal unterstützt einen Titel
-GameServer.Log("MSCO dedicated server " + GameServer.ModVersion + " (" + RuntimeInformation.OSDescription + ")");
+GameServer.Log("MSCO dedicated server " + Updater.CurrentVersion + " for MSCO mod " + GameServer.ModVersion + " (" + RuntimeInformation.OSDescription + ")");
 GameServer.Log("Data folder: " + dataDir);
 GameServer.Log("Master server: " + MasterServer.Url);
 
@@ -138,7 +140,8 @@ using var sigterm = PosixSignalRegistration.Create(PosixSignal.SIGTERM, ctx => {
 using var sigquit = PosixSignalRegistration.Create(PosixSignal.SIGQUIT, ctx => { ctx.Cancel = true; host.RequestExit(); });
 
 int exitCode = host.Run();
-if (exitCode != 0) Pause();
+if (exitCode == Updater.RestartExitCode) Updater.Relaunch(args);
+else if (exitCode != 0) Pause();
 return exitCode;
 
 string ArgValue(string name)