tests: add a frontend i18n hardcoded-string smoke check

[Senzo13]

Context

JoyBoy has a growing frontend and it is easy to accidentally add French-only strings directly in JS templates.

Relevant files:

• tests/
• web/static/js/i18n.js
• web/static/js/chat.js
• web/static/js/generation.js
• web/static/js/settings.js

Suggested approach

Add a lightweight test or script that scans selected frontend files for common hardcoded French UI words in template strings and suggests using translation helpers.

Acceptance criteria

• The check is intentionally small and has an allowlist for comments/logs if needed.
• It catches obvious hardcoded UI strings such as button labels and titles.
• It does not fail on translation definitions inside i18n.js.
• The test can be run with python -m unittest discover -s tests -p "test_*.py".