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.

README.md

@@ -14,6 +14,12 @@ This project is based on source code of Minecraft Legacy Console Edition v1.6.05
 
 ## Latest:
 
+Dedicated server biome diversity fix:
+- The dedicated server previously used a completely random seed with no biome diversity checks — unlike the client which validates seeds to guarantee varied biomes. This could result in server worlds with large regions dominated by only one or two biome types (e.g. all taiga/snowy)
+- On top of that, the client's seed validation was hardcoded to only check a 54-chunk (Classic) area, so even validated seeds had no diversity guarantee beyond that — making the problem especially noticeable on Large worlds or worlds expanded from Classic to Large
+- New server worlds now validate seeds for biome diversity, and the validation scales to the full target world size
+- Added `override-seed` in server.properties to fix existing worlds without deleting them — set it to any seed number and newly generated chunks will use it instead of the original
+
 Server list and connection improvements:
 - Server edits and deletions now apply immediately without needing to restart the game
 - Connecting to an offline/unreachable server no longer freezes the game indefinitely