refactor: Phase 0 — 清除重复，委托 @pkmn 生态

- 删除硬编码 NATURES 常量，nature.ts 委托 Dex.natures
- 删除硬编码 EVOLUTION_CHAINS，evolution.ts 委托 Dex.species.evos
- calculateStats() 手写公式替换为 gen.stats.calc()
- 统一 TO_DEX_STAT/FROM_DEX_STAT 映射到 pkmn.ts
- 简化 species.ts buildEvolutionChain() 复用 getNextEvolution()
- 添加 NatureName/NatureEffect 类型定义

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/pokemon/src/index.ts

@@ -1,6 +1,9 @@
 // Types
 export type {
 	StatName,
+	NatureName,
+	NatureStat,
+	NatureEffect,
 	SpeciesId,
 	Gender,
 	EvolutionTrigger,
@@ -23,7 +26,9 @@ export { SPECIES_DATA, DEX_TO_SPECIES, getSpeciesData, getAllSpeciesData, ensure
 export { DEFAULT_EV_MAPPING, getEVForTool, MAX_EV_PER_STAT, MAX_EV_TOTAL } from './data/evMapping'
 export { xpForLevel, levelFromXp, xpToNextLevel } from './data/xpTable'
 export { SPECIES_NAMES, SPECIES_I18N, SPECIES_PERSONALITY } from './data/names'
+export { getAllNatureNames, randomNature, getNatureEffect } from './data/nature'
 export { getNextEvolution, EVOLUTION_CHAINS } from './data/evolution'
+export { FROM_DEX_STAT, TO_DEX_STAT } from './data/pkmn'
 
 // Core
 export { generateCreature, calculateStats, getCreatureName, recalculateLevel, getActiveCreature, getTotalEV } from './core/creature'