Implement persistent hardcore death bans (XUID + IP) for dedicated server

On the dedicated server, hardcore death now persists XUID and IP bans to
banned-players.json and banned-ips.json via the Access system, and
disconnects the player. Bans survive server restarts. Client-hosted games
retain the existing in-memory XUID ban with force-save behavior.

- Add hardcore property to server.properties (forces Hard difficulty)
- Add LevelData::setHardcore() so loaded worlds respect the server config
- Add PlayerList::banPlayerForHardcoreDeath() with persistent XUID + IP bans
- Reject respawn requests server-side in hardcore mode
- Ensure server-side player ticks run without move packets (fixes
  environmental damage not applying for some clients)
- Restore 0x8 hardcore bit on LoginPacket/RespawnPacket wire format so
  the client-side death screen detects hardcore mode correctly

Minecraft.Server/ServerProperties.cpp

@@ -54,6 +54,7 @@ static const ServerPropertyDefault kServerPropertyDefaults[] =
 	{ "gamemode", "0" },
 	{ "gamertags", "true" },
 	{ "generate-structures", "true" },
+	{ "hardcore", "false" },
 	{ "host-can-be-invisible", "true" },
 	{ "host-can-change-hunger", "true" },
 	{ "host-can-fly", "true" },
@@ -861,6 +862,7 @@ ServerPropertiesConfig LoadServerPropertiesConfig()
 	config.doTileDrops = ReadNormalizedBoolProperty(&merged, "do-tile-drops", true, &shouldWrite);
 	config.naturalRegeneration = ReadNormalizedBoolProperty(&merged, "natural-regeneration", true, &shouldWrite);
 	config.doDaylightCycle = ReadNormalizedBoolProperty(&merged, "do-daylight-cycle", true, &shouldWrite);
+	config.hardcore = ReadNormalizedBoolProperty(&merged, "hardcore", false, &shouldWrite);
 
 	config.maxBuildHeight = ReadNormalizedIntProperty(&merged, "max-build-height", 256, 64, 256, &shouldWrite);
 	config.motd = ReadNormalizedStringProperty(&merged, "motd", "A Minecraft Server", 255, &shouldWrite);

Minecraft.Server/ServerProperties.h

@@ -73,6 +73,7 @@ namespace ServerRuntime
 		bool doTileDrops;
 		bool naturalRegeneration;
 		bool doDaylightCycle;
+		bool hardcore;
 
 		/** other MinecraftServer runtime settings */
 		int maxBuildHeight;

Minecraft.Server/Windows64/ServerMain.cpp

@@ -369,6 +369,13 @@ int main(int argc, char **argv)
 	ServerPropertiesConfig serverProperties = LoadServerPropertiesConfig();
 	ApplyServerPropertiesToDedicatedConfig(serverProperties, &config);
 
+	// Hardcore mode forces Hard difficulty (matches vanilla Java behavior)
+	if (serverProperties.hardcore && serverProperties.difficulty != 3)
+	{
+		LogInfof("startup", "Hardcore mode enabled: forcing difficulty from %d to 3 (Hard).", serverProperties.difficulty);
+		serverProperties.difficulty = 3;
+	}
+
 	if (!ParseCommandLine(argc, argv, &config))
 	{
 		PrintUsage();
@@ -529,6 +536,7 @@ int main(int argc, char **argv)
 	app.SetGameHostOption(eGameHostOption_DoTileDrops, serverProperties.doTileDrops ? 1 : 0);
 	app.SetGameHostOption(eGameHostOption_NaturalRegeneration, serverProperties.naturalRegeneration ? 1 : 0);
 	app.SetGameHostOption(eGameHostOption_DoDaylightCycle, serverProperties.doDaylightCycle ? 1 : 0);
+	app.SetGameHostOption(eGameHostOption_Hardcore, serverProperties.hardcore ? 1 : 0);
 #ifdef _LARGE_WORLDS
 	app.SetGameHostOption(eGameHostOption_WorldSize, serverProperties.worldSize);
 	// Apply desired target size for loading existing worlds.