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.Server/Security/RateLimiter.h

@@ -0,0 +1,47 @@
+#pragma once
+
+#include <string>
+#include <deque>
+#include <unordered_map>
+
+#ifdef _WINDOWS64
+#include <Windows.h>
+#endif
+
+namespace ServerRuntime
+{
+	namespace Security
+	{
+		class RateLimiter
+		{
+		public:
+			RateLimiter();
+			~RateLimiter();
+
+			RateLimiter(const RateLimiter &) = delete;
+			RateLimiter &operator=(const RateLimiter &) = delete;
+			RateLimiter(RateLimiter &&) = delete;
+			RateLimiter &operator=(RateLimiter &&) = delete;
+
+			/**
+			 * Returns true if the connection from this IP should be allowed.
+			 * Returns false if the IP has exceeded maxPerWindow connections within windowMs milliseconds.
+			 */
+			bool AllowConnection(const std::string &ip, int maxPerWindow, int windowMs);
+
+			/**
+			 * Removes stale entries older than evictionAgeMs from the tracking map.
+			 */
+			void EvictStale(int evictionAgeMs = 300000);
+
+		private:
+			CRITICAL_SECTION m_lock;
+			std::unordered_map<std::string, std::deque<ULONGLONG>> m_connectionTimes;
+		};
+
+		/**
+		 * Global rate limiter instance for the dedicated server accept loop.
+		 */
+		RateLimiter &GetGlobalRateLimiter();
+	}
+}