Fix public website auth links that resolve to localized 404s

[Hmbown]

Observed

On 2026-08-30, these public Codewhale website routes resolve after localization to 404:

• https://codewhale.net/signin -> https://codewhale.net/en/signin
• https://codewhale.net/signup -> https://codewhale.net/en/signup
• https://codewhale.net/auth/callback -> https://codewhale.net/en/auth/callback

Product boundary

This is a Codewhale public-site routing/link issue. The signed-in CWC application uses https://app.codewhale.net/login and must remain a separate authority; do not duplicate or migrate CWC auth into this repository.

Acceptance

• Public auth-oriented CTAs lead to the intended account-entry destination or a truthful public explanation.
• Localized paths do not land on 404.
• Browser verification records the exact deployed revision and final destination.
• The change does not claim a real CWC registration or OAuth lifecycle; that remains CWC Phase C: sub-agent context-passing audit — minimize what's stringified between parent and child #305.