feat(auth): implement email verification process with resend functionality and update registration flow

app/api/auth/verify-email/resend/route.ts

@@ -0,0 +1,55 @@
+import { NextRequest } from 'next/server';
+import { db } from '@/lib/db';
+import { checkRateLimit, getClientIp } from '@/lib/rate-limit';
+import { apiErrors, successResponse, withCacheControl } from '@/lib/api-response';
+import { createVerificationToken, isEmailVerificationEnabled, sendVerificationEmail } from '@/lib/email-verification';
+import { logError } from '@/lib/logger';
+
+export async function POST(request: NextRequest) {
+    try {
+        if (!isEmailVerificationEnabled()) {
+            return apiErrors.badRequest('Email verification is not enabled');
+        }
+
+        // Rate-limit by IP to prevent abuse
+        const clientIp = getClientIp(request);
+        const rateLimitResult = await checkRateLimit(`resend-verification:${clientIp}`, 'resend-verification');
+        if (!rateLimitResult.allowed) {
+            return apiErrors.rateLimited('Too many requests. Please try again later.');
+        }
+
+        const body = await request.json();
+        const { email } = body;
+
+        if (!email || typeof email !== 'string' || email.length > 254 || !email.includes('@')) {
+            return apiErrors.badRequest('Valid email is required');
+        }
+
+        const normalizedEmail = email.toLowerCase().trim();
+
+        const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
+        if (!emailRegex.test(normalizedEmail)) {
+            return apiErrors.badRequest('Valid email is required');
+        }
+
+        // Look up user — return a generic success regardless of whether the email
+        // exists to avoid user enumeration
+        const user = await db.user.findUnique({
+            where: { email: normalizedEmail },
+            select: { id: true, emailVerified: true },
+        });
+
+        if (user && !user.emailVerified) {
+            const token = await createVerificationToken(normalizedEmail);
+            await sendVerificationEmail(normalizedEmail, token);
+        }
+
+        return withCacheControl(
+            successResponse({ message: 'If that email has an unverified account, a new verification link has been sent.' }),
+            'private, no-store'
+        );
+    } catch (err) {
+        logError('Resend verification error:', err);
+        return apiErrors.internalError('Failed to resend verification email');
+    }
+}