Fix: signup dev UX when verification email fails (Fixes #3901)

[Nixxx19]

Fixes #3901

Changes

In non-production (dev/local), when the verification email fails to send (e.g. Mailgun not in .env), the server now still returns 200 and the user payload so the client can redirect and log the user in. This makes signup UX in dev match production when email is configured.

• Prod: Unchanged. Mail failure still returns 500.
• Dev: Mail failure no longer blocks success; user is redirected to home and logged in.

Single file: server/controllers/user.controller/signup.ts, in the mail-send catch block, return success when NODE_ENV !== 'production'.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• has no typecheck errors (npm run typecheck)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #3901
• meets the standards outlined in the accessibility guidelines

Screen.Recording.2026-02-17.at.12.00.24.PM.mov

[Nixxx19]

Hi @raclim, I've tested the changes locally and the PR is ready for review! Whenever it's convenient for you, please take a look. Thanks!