Server 2.10.4: HTTPS for the web panel and hostile client hardening

- Panel over HTTPS on the game port (TLS handshake detected like HTTP); self-signed
  certificate in data/panel_cert.pfx (fingerprint in the log) or an own PFX
  (PanelCertificatePath); remote HTTP is redirected to HTTPS (not locally / behind
  a proxy); cookie Secure over HTTPS; PanelHttps=false turns it off
- Panel login: also locked per user name (16 failures / 15 min), failure lists
  bounded, user names in the log without control characters
- panel_users.json, panel_sessions.json, server.json, certificate: owner-only on Linux
- Players: names/chat without control or direction characters (no fake log lines),
  no '<' '>' in names; '* ' system-style chat, msco.* messages (time/weather) and
  MSCO_INSTALL only from admins; NaN/absurd money changes dropped (could break the
  shared money for good)
- Extra headers: Permissions-Policy, Cross-Origin-Opener-Policy
- 11 new tests (165 pass)

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

PanelUsers.cs

@@ -146,6 +146,7 @@ public sealed class PanelUsers
     {
         string tmp = path + ".tmp";
         File.WriteAllText(tmp, JsonSerializer.Serialize(new FileData { Users = users }, Options));
+        PanelTls.Restrict(tmp); // Passwort-Hashes nur für den Server-Benutzer lesbar (Linux)
         if (!OperatingSystem.IsWindows())
             try { File.SetUnixFileMode(tmp, UnixFileMode.UserRead | UnixFileMode.UserWrite); } catch { }
         File.Move(tmp, path, true);