Add seed validation for server world creation and override-seed property

The dedicated server previously picked a completely random seed with no
biome diversity checks (the client validates but the server skipped it).
On top of that, the client's findSeed() was hardcoded to only check a
54-chunk (Classic) area, so Large worlds had no diversity guarantee
beyond the center.

New server worlds now use findSeed() scaled to the full target world
size. Added override-seed in server.properties to fix existing worlds
without deleting them.

Minecraft.Server/ServerProperties.h

@@ -31,6 +31,9 @@ namespace ServerRuntime
 		bool hasSeed;
 		/** `level-seed` */
 		__int64 seed;
+		/** `override-seed` replaces the seed for biome generation on existing worlds */
+		bool hasOverrideSeed;
+		__int64 overrideSeed;
 		/** `log-level` */
 		EServerLogLevel logLevel;
 		/** `autosave-interval` (seconds) */