E2E: lang switch matrix on root pages

[wab]

Parent

#121

What to build

Playwright parametrized test: for each root page (home, about, method, blog, jobs, clients, contact), switch FR ↔ EN and assert URL + content swap.

Acceptance criteria

• Reuses Playwright setup from Test: Playwright setup + homepage golden path E2E #134
• Parametrized over root pages
• Asserts URL prefix change and at least one localized string per page
• Test passes in CI

Blocked by

• Test: Playwright setup + homepage golden path E2E #134