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/ServerProperties.h

@@ -80,6 +80,24 @@ namespace ServerRuntime
 		/** `hardcore-ban-ip` — whether hardcore death bans include IP bans */
 		bool hardcoreBanIp;
 
+		/** security settings */
+		/** `hide-player-list-prelogin` — strip XUIDs from PreLoginPacket response */
+		bool hidePlayerListPreLogin;
+		/** `rate-limit-connections-per-window` — max TCP connections per IP within the rate limit window */
+		int rateLimitConnectionsPerWindow;
+		/** `rate-limit-window-seconds` — sliding window duration for connection rate limiting */
+		int rateLimitWindowSeconds;
+		/** `max-pending-connections` — max simultaneous pending (pre-login) connections */
+		int maxPendingConnections;
+		/** `require-challenge-token` — reserved for future protocol extension (not yet enforced) */
+		bool requireChallengeToken;
+		/** `enable-stream-cipher` — enable XOR stream cipher for traffic obfuscation */
+		bool enableStreamCipher;
+		/** `require-secure-client` — kick clients that do not complete the cipher handshake */
+		bool requireSecureClient;
+		/** `proxy-protocol` — parse PROXY protocol v1 headers from TCP tunnel (e.g. playit.gg) */
+		bool proxyProtocol;
+
 		/** other MinecraftServer runtime settings */
 		int maxBuildHeight;
 		std::string levelType;