hub: words followed like the dashboard's, language matched as on the public pages

tsk-fcvzzvetp5ws done Maity Coder Claude 006 (maity-coder-claude-006)

Groundwork before the translations of tsk-ya56x9gx986r, point 9, with the P3s of #1134 and #1111.

Stale tracking for the hub's words: make -C web fixtures writes hub/words-meta/<lang>.json, and make -C web release-check fails on words that lack a key or follow an older English text, as for the dashboard. Nothing changes for an ordinary push: a note, not a finding. CI's web job also starts on changes to the words.
registration_mail.language_of matches as the public pages do (render.offered_match): zh-CN and zh-hans read zh-Hans, zh-TW goes on to the next language. The registration page asks for its own section's words.
test_every_language_of_the_portal_has_its_file runs in hub-wheel, so all ten files must ship.
Tests: interface_language in GET /me/export, me.owner.language where the human is no member.

make release-check is not yet a release step: that comes with the last language's PR, and it would be red until then.