feat(i18n): multi-language support

[SurviveM]

Requirement

Extract all hardcoded UI strings into i18n.dict.mjs (existing foundation). Add Japanese, Korean, Traditional Chinese translations. Language switcher in top-right corner, persists user choice.

Verification

1. Switch language to "Japanese" -> all UI labels change to Japanese -> refresh page -> language stays Japanese
2. Switch to Korean -> verify all panels display Korean text consistently
3. Switch back to Chinese -> all labels restore correctly