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>

pack/mods/spark.pw.toml

@@ -0,0 +1,17 @@
+name = "spark"
+filename = "spark-1.10.124-neoforge.jar"
+side = "server"
+
+[download]
+url = "https://cdn.modrinth.com/data/l6YH9Als/versions/v5qtqRQi/spark-1.10.124-neoforge.jar"
+hash-format = "sha512"
+hash = "f86ce34f2759c69df82578c397ff55b666c84626229a98f598458b960c21b38c95d6bfef4772af7f963c4f4868e5e2d9aef6b99c1d51bab55bf45e0e6e6b5ed4"
+
+[update]
+[update.modrinth]
+mod-id = "l6YH9Als"
+version = "v5qtqRQi"
+
+[update.curseforge]
+file-id = 6225208
+project-id = 361579