Phase 9: reproducible builds, balance from the server, spark check, play feedback

Build: every tool pinned (JDK, packwiz, Gradle plugins, Python packages), exports
normalised, tools/check_reproducible.py proves two clean builds are byte-identical.

Server-side balance: a server can load config/cobblesurvival/datapack.zip in place of
the jar's data, /reload applies it, tools/server_update.py packages it and refuses
when a client change is needed. JEI drop pages are sent by the server. Code-held
balance numbers moved to tuning/server.json.

Performance: spark in the pack (server only), tools/perf_test.py with fake players
whose chunks really are active, docs/performance.md.

Adrian's feedback: default keys R, U, J, §; drop pages link to Cobblemon Info and show
real chances; bosses only hurt in battles; battle XP halved; channels between the
islands low level; temperature ×3 with insulation doubled; hazards start at once; no
item dots on the map; a wild attack starts a battle; the starter only faints; quest
book on join with a basics page and an HMs page; regional forms obtainable.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/mcserver.py

@@ -15,6 +15,7 @@ import tomllib
 import urllib.request
 from pathlib import Path
 
+import lock
 from packwiz_sync import java, sync
 
 ROOT = Path(__file__).resolve().parent.parent
@@ -82,8 +83,7 @@ def prepare():
     SERVER.mkdir(parents=True, exist_ok=True)
     args_file = SERVER / "libraries/net/neoforged/neoforge" / version / "unix_args.txt"
     if not args_file.exists():
-        installer = download(f"https://maven.neoforged.net/releases/net/neoforged/neoforge/{version}/"
-                             f"neoforge-{version}-installer.jar", CACHE / f"neoforge-{version}-installer.jar")
+        installer = lock.download(f"neoforge-{version}-installer.jar")
         subprocess.run([java(), "-jar", str(installer), "--install-server", str(SERVER)],
                        cwd=SERVER, check=True, stdout=subprocess.DEVNULL)
     sync("server", SERVER, BUILD / "stage" / "full")