Update register view with Tailwind

[BojayL]

Summary

• Refactor the register form to use Tailwind utility classes instead of the shared form CSS module.
• Preserve the existing sign-up flow, email validation, password visibility toggle, login link, and error rendering.
• Add accessible labels and button semantics for the email/password inputs and visibility control.

Closes #50

Validation

• yarn workspace frontend build
• npm --workspace frontend run build
• npx playwright screenshot --viewport-size=1440,900 http://localhost:3100/sign-up /tmp/corecode-signup-desktop.png
• npx playwright screenshot --viewport-size=390,844 http://localhost:3100/sign-up /tmp/corecode-signup-mobile.png
• git diff --check

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