Decode the \u-escaped zh-Hant block to literal Traditional Chinese and backfill
missing keys so zh-Hant has full coverage of the en key set (verified: 0 en keys
missing from zh-Hant). Preserves the v0.51.212 #3396 session_title_regenerate*
translations (not reverted to English). Locale-only, no runtime behavior change.
Co-authored-by: Peter Dave Hello <hsu@peterdavehello.org>
