#226: R7: Separate i18n translation data from logic

[github-actions]

Closes #226

Summary

This PR splits the monolithic src/i18n.ts file (300 lines) into a directory module to separate translation data (~200 lines) from logic functions.

Changes:

• Created src/i18n/ directory module
• Moved translation map data to src/i18n/translations.ts (237 lines)
• Moved logic functions to src/i18n/index.ts (85 lines)
• Relocated and updated test file to src/i18n/i18n.test.ts with corrected imports
• Deleted old src/i18n.ts file

Backward compatibility:

• All existing imports like from "./i18n" continue to work via directory module resolution
• All exports maintain exact same types and signatures
• No breaking changes for consumers

Verification:

• ✅ npm run lint - passed
• ✅ npm run typecheck - passed
• ✅ npm run build - passed
• ✅ npm test - all 398 tests passed