phsl / new-api

* fix(i18n): add missing frontend translations

- add missing locale entries for API key loading, channel model empty states, auth, playground, and model configuration copy.
- correct inaccurate Russian and Vietnamese model empty-state translations to avoid fallback or misleading copy.

* fix(auth): align password validation copy

- remove the login password length gate so existing shorter passwords are not blocked before reaching the server.
- reuse distinct minimum-length and 8-20 character messages based on the actual validation rule.
- drop unused duplicate password locale keys and align the user creation placeholder with the 8-20 character constraint.

* fix(i18n): add auth validation message translations

- cover schema-driven auth form errors that are translated through FormMessage.
- keep password, username, confirmation, and OTP validation messages available in every locale.