fix: show the real signup error instead of "Unexpected Error"

[hassan1brahim]

What was done

• Replaced the res_json.body check in SignUp with res_json.message in app/lib/actions.ts
• Added a signupErrorMessage helper that maps the errors /create returns to clearer signup messages
• Passed unrecognized backend messages through instead of replacing them with a generic error
• Kept Unexpected Error only when the backend sends no message

Why

Every failed signup was showing Unexpected Error.

The frontend was reading res_json.body, but body is part of the Lambda → API Gateway response envelope. API Gateway consumes that wrapper, so the frontend actually receives:

{
  statusCode: 400,
  message: 'Duplicate user!'
}

That meant res_json.body was always undefined and every failure fell back to the generic error.

This change reads message instead and maps the known /create errors to clearer, actionable messages. Matching uses lowercased substrings rather than exact strings because the backend wiki and handler differ slightly in wording.

Closes #342

[vercel]

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Project	Deployment	Actions	Updated
frontendv2	Ready	Preview	Sep 15, 2026 1:30pm UTC