Add zh-TW as a new supported language, covering all 1500+ translation keys
with Taiwan-standard terminology and phrasing.
Changes:
- src/i18n/locales/zh-TW.json: new file, full Traditional Chinese translation
- src/i18n/index.ts: import and register zh-TW locale
- src/types/common.ts: add 'zh-TW' to Language union type
- src/utils/constants.ts: add zh-TW to LANGUAGE_ORDER and LANGUAGE_LABEL_KEYS
- src/utils/language.ts: add zh-tw/zh-hant browser locale detection
- src/i18n/locales/*.json: add chinese_tw label key to all locales
Co-authored-by: lmanchu <lman.chu@gmail.com>