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/cobblebase_loot.py

@@ -19,6 +19,8 @@ import sys
 import zipfile
 from pathlib import Path
 
+import lock
+
 ROOT = Path(__file__).resolve().parent.parent
 OUT = ROOT / "datapacks/core/data/cobblebase/loot_table"
 CONDITION = "cobblesurvival:in_zone"
@@ -48,10 +50,7 @@ FAMILIES = {
 
 
 def cobblebase_jar():
-    jars = sorted((ROOT / "build/server/mods").glob("cobblebase-*.jar"))
-    if not jars:
-        sys.exit("no Cobblebase jar in build/server/mods: run tools/build.py and tools/selftest.py (or the quick check) first")
-    return jars[-1]
+    return lock.mod_jar("cobblebase")
 
 
 def zone_items():