fix: don't require email infra on self-hosted, improve login form detection

- sendTransactionalEmail no-ops (with a warning) when no mail transport is
  configured instead of throwing — sign-up 500'd on SMTP-less instances
- sendVerificationEmail catches transport failures so a broken SMTP can't
  block account creation; verification stays optional (requireEmailVerification
  was never set)
- login form gains id/name attributes and label for/id pairing so password
  managers (Proton Pass et al.) detect the fields; email input uses
  autocomplete=username

Authored By: TDvorak <[email protected]>

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/frontend/src/App.tsx

@@ -736,7 +736,7 @@ export default function App() {
       try {
         if (mode() === "sign-up") {
           await authClient.signUp.email({ email: email(), password: password(), name: name() });
-          setAuthMessage("Account created. Check Mailpit (or your SMTP provider) for the verification email.");
+          setAuthMessage("Account created — signing you in.");
         } else {
           await authClient.signIn.email({ email: email(), password: password() });
         }