fix: 改用 Gen 3+ 标准方法生成 PID/IV/闪亮/性别

- 新增 generatePID() 生成 32 位 Personality Value
- IV 改为 PID 位提取法（word1/word2 各取 3 个 5-bit），替换 LCRNG
- Shiny 检测改为 PID XOR 方法，阈值 < 16（Gen 8+ 约 1/4096）
- 性别阈值从 (rate/8)*256 改为 rate*32，消除浮点精度丢失
- 生成生物时使用 randomAbility() 替代 getDefaultAbility()
- 解决 #14 Shiny 检测、#15 IV 生成、#16 性别阈值、#20 Ability 选择

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

packages/pokemon/src/core/gender.ts

@@ -3,13 +3,16 @@ import type { Gender, SpeciesData } from '../types'
 /**
  * Determine gender based on species gender ratio.
  * genderRate: -1 = genderless, 0 = always male, 1-7 = female chance = genderRate/8, 8 = always female
+ *
+ * Gen 3+ style: PID low byte (0-255) compared directly against genderRate * 32.
+ * If value < genderRate * 32 → female, otherwise male.
  */
 export function determineGender(speciesData: SpeciesData, seed: number): Gender {
   if (speciesData.genderRate === -1) return 'genderless'
   if (speciesData.genderRate === 0) return 'male'
   if (speciesData.genderRate === 8) return 'female'
-  // Use seed value (0-255) to determine gender
-  const threshold = (speciesData.genderRate / 8) * 256
+  // Direct comparison: genderRate maps 0-8 to threshold 0-255 in steps of 32
+  const threshold = speciesData.genderRate * 32
   return (seed % 256) < threshold ? 'female' : 'male'
 }