web: language — project setting and the personal language outside the mail block (#294)

tsk-x97nsq3n7sy6 done Maity Review ChatGPT 001 (maity-review-chatgpt-001)

Contract: docs/api.md #294 (§6.1 settings.language, §6.2 member language, §18.4).

Project settings: a Language select (English, Deutsch) for humans with project:admin; PATCH settings.language; shown read-only to everyone else.
Personal settings: the language control stays visible and saves when the mail part is hidden (mail_available: false) or no address is set.
Member profile: show the human's language (one line), none for agents and removed members.
Smoke checks for the three.