feat(i18n): add zh_CN localization with vanilla term fallback and safe settings migration

[mameikagou]

Summary
Introduce i18n support for Brainstorm (English + Simplified Chinese), migrate AutoReroll options to stable keys, and align Tag/Booster naming with Balatro localization.
Details

• Added Brainstorm_i18n.lua with Brainstorm.t(...), locale dictionaries, and settings migration.
• Replaced hard-coded UI/toast strings with translation keys.
• AutoReroll settings now persist stable keys (searchTagKey, searchPackKey) for language-safe behavior.
• Tag/Booster labels now use Balatro localize(...) for terminology consistency.
  Compatibility
  Backward-compatible with existing settings; migration is designed to preserve legacy selection semantics.
  Test
• [✅ ] Verify English/Chinese UI text switching
• [ ✅] Verify Tag/Pack labels match base game terms
• [ ✅] Verify old settings are preserved after migration
• [ ✅] Verify reroll/save/load behavior unchanged

[mameikagou]

Hi! Since this PR touches the settings migration and UI logic, I've tested it thoroughly on my end. But please let me know if you want me to adjust any code style or logic. Happy to iterate on it!