feat(bans): Windows blocklist gate with demand-paged promotion

Enforce a millions-strong external IP blocklist in-app so the OS firewall
never has to hold it (Windows BFE can't). FileBlocklist loads a versioned
file into an immutable SortedRangeIndex snapshot off the game loop (yields to
world saves) and swaps it atomically; the accept path gates against it after
the manual-ban check and, once per suppression window (PromotedGuard),
promotes the hit to CrowdSec (scenario modernuo/blocklist) so the OS bouncer
kernel-drops repeat traffic. The bulk list is produced entirely out-of-process.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Projects/Server/Network/Bans/Blocklist/PromotedGuard.cs

@@ -0,0 +1,55 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: PromotedGuard.cs                                                *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Collections.Generic;
+
+namespace Server.Network.Bans.Blocklist;
+
+/// <summary>Suppresses re-reporting the same IP within a TTL. Accept-path thread only.</summary>
+public sealed class PromotedGuard
+{
+    private readonly Dictionary<UInt128, long> _expiry = new();
+
+    public bool TryMark(UInt128 ip, long nowTicks, long ttlMs)
+    {
+        if (_expiry.TryGetValue(ip, out var exp) && exp - nowTicks > 0)
+        {
+            return false;
+        }
+        _expiry[ip] = nowTicks + ttlMs;
+        return true;
+    }
+
+    public void Sweep(long nowTicks)
+    {
+        if (_expiry.Count == 0)
+        {
+            return;
+        }
+        using var dead = Collections.PooledRefQueue<UInt128>.Create();
+        foreach (var (ip, exp) in _expiry)
+        {
+            if (exp - nowTicks <= 0)
+            {
+                dead.Enqueue(ip);
+            }
+        }
+        while (dead.Count > 0)
+        {
+            _expiry.Remove(dead.Dequeue());
+        }
+    }
+}