feat: dedicated server security hardening

Comprehensive security system to protect against packet-sniffing attacks,
XUID harvesting, privilege escalation, bot flooding, and XUID impersonation.

- Stream cipher: per-session XOR cipher with 4-message handshake via
  CustomPayloadPacket (MC|CKey, MC|CAck, MC|COn). Negotiated per-connection,
  backwards compatible (old clients/servers fall back to plaintext).
- Security gate: buffers all game data until cipher handshake completes,
  preventing unsecured clients from receiving any XUIDs or game state.
- Cipher handshake enforcer: kicks clients that don't complete the handshake
  within 5 seconds (configurable via require-secure-client).
- Identity tokens: persistent per-XUID tokens in identity-tokens.json,
  issued over the encrypted channel, verified on reconnect. Prevents XUID
  replay attacks. Client stores server-specific tokens.
- PROXY protocol v1: parses real client IPs from playit.gg tunnel headers
  so rate limiting, IP bans, and XUID spoof detection work per-player.
- Rate limiting: per-IP sliding window (default 5 connections/30s) with
  pending connection cap (default 10).
- Privilege hardening: OP requires ops.json, live checks on every command
  and privilege packet. Host-only server settings changes.
- XUID stripping: PreLoginPacket response sends INVALID_XUID placeholders.
- Packet validation: readUtf global string cap, reduced max packet size,
  stream desync protection on oversized strings.
- OpManager: persistent ops.json with XUID-based OP list.
- Whitelist improvements: whitelist add accepts player names with ambiguity
  detection, XUID cache from login attempts.
- revoketoken command: revoke identity tokens for players who lost theirs.
- server.log: persistent log file written alongside console output with
  flush-per-write to survive crashes.
- CLI security logging: consolidated per-join security summary with cipher
  status, token status, XUID, and real IP. Security warnings for kicks,
  spoofing, and unauthorized commands.

Minecraft.Client/ServerConnection.cpp

@@ -10,6 +10,10 @@
 #include "..\Minecraft.World\Socket.h"
 #include "..\Minecraft.World\net.minecraft.world.level.h"
 #include "MultiPlayerLevel.h"
+#if defined(_WINDOWS64) && defined(MINECRAFT_SERVER_BUILD)
+#include "..\Minecraft.Server\Security\SecurityConfig.h"
+#include "..\Minecraft.Server\ServerLogManager.h"
+#endif
 
 ServerConnection::ServerConnection(MinecraftServer *server)
 {
@@ -40,6 +44,17 @@ void ServerConnection::addPlayerConnection(shared_ptr<PlayerConnection> uc)
 void ServerConnection::handleConnection(shared_ptr<PendingConnection> uc)
 {
 	EnterCriticalSection(&pending_cs);
+#if defined(_WINDOWS64) && defined(MINECRAFT_SERVER_BUILD)
+	int maxPending = ServerRuntime::Security::GetSettings().maxPendingConnections;
+	if (maxPending > 0 && static_cast<int>(pending.size()) >= maxPending)
+	{
+		LeaveCriticalSection(&pending_cs);
+		app.DebugPrintf("SECURITY: Rejecting connection, too many pending (%d/%d)\n",
+			static_cast<int>(pending.size()), maxPending);
+		uc->disconnect(DisconnectPacket::eDisconnect_ServerFull);
+		return;
+	}
+#endif
 	pending.push_back(uc);
 	LeaveCriticalSection(&pending_cs);
 }