Phase 3: soft level pressure, less experience far above a zone's band

- Companion mod (zone/LevelPressure.kt): a Pokemon more than 5 levels
  above the band of the zone its trainer is in gets 10% less experience
  per extra level, down to 10%. Exp. Candy and commands are exempt; no
  hard level caps (roadmap).
- Rules in world/zones.json -> level_pressure, shipped in the zone layout.
- Self-test level_pressure_cuts_xp.

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

docs/balance.md

@@ -27,6 +27,7 @@ Every tunable lives in a config file or in this table. **Placeholder** means gue
 | Guardian strength | strongest Pokémon spawning in the zone, band top + 5 levels, 1.5× size, uncatchable | Placeholder | `tools/zone_spawns.py` (`GUARDIAN_*`), `world/zones.json` → `guardian.species` | |
 | Guardian drops | Button Isle 10 Poké Balls + 4 Potions; Southwold 6 Great Balls + 4 Exp. Candy S; Westmarch and Jungle Mire Waders + 4 Pecha Berries + 2 Exp. Candy M; Mire and Highlands 3 Icy Rocks + 4 Super Potions; Sunscorch 3 Heat Rocks + 2 Exp. Candy L; Frostpeak and Deep Dark 3 Icy Rocks + 2 Exp. Candy L; Deep Sea Mystic Water + 3 Exp. Candy M | Placeholder | `world/zones.json` → `guardian.drops` | 3 rocks make one full fur or hide set |
 | Mire poison | Poison I for 7 s, renewed every 5 s while in the Mire without Mire Waders | Placeholder | `datapacks/core/data/cobblesurvival/zone_hazards/mire.json` | Vanilla Poison stops at half a heart |
+| Level pressure | full experience up to 5 levels above the zone's band, then 10 % less per level, at least 10 % (Exp. Candy and commands exempt) | Placeholder | `world/zones.json` → `level_pressure` | E.g. on Button Isle (up to Lv 10): Lv 15 full, Lv 20 half, Lv 24+ a tenth |
 | Healing while sleeping | off (`healPercent` 0) | Decided (roadmap) | `config/cobblemon/main.json` | |
 | Loot container refresh | 1 hour (72,000 ticks of game time) after first opened, all containers | Decided (Adrian, 2026-10-29) | `config/lootr-common.toml` | Tiering by structure/biome later |
 | Gamerules in the template | `doMobSpawning false` | Decided (Adrian, 2026-10-28; may be reverted later) | `world/world.json` → `gamerules` | Pokémon spawning is Cobblemon's own `doPokemonSpawning` |