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/config/cobblemon/main.json

@@ -38,7 +38,7 @@
   "awardExperienceOnBattleLoss": false,
   "luckyEggMultiplier": 1.5,
   "allowSpectating": true,
-  "experienceMultiplier": 2.0,
+  "experienceMultiplier": 1.0,
   "predationChance": 0.05,
   "pokemonPerChunk": 1.0,
   "pokeSnackPokemonPerChunk": 2.0,