auth: build verification link from BASE_URL env var

- Build the verification URL as /api/auth/verify-email?token=xxx&callbackURL=/login
- Pass token from Better Auth callback instead of its built-in url
- Add callbackURL=/login so user lands on login after verifying

src/lib/auth.ts

@@ -13,10 +13,10 @@ export const auth = betterAuth({
 	}),
 	emailVerification: {
 		sendOnSignUp: true,
-		sendVerificationEmail: async ({ user, url }) => {
+		sendVerificationEmail: async ({ user, token }) => {
 			void sendVerificationEmail({
 				email: user.email,
-				verificationUrl: url
+				token
 			});
 		}
 	},

src/lib/server/email-verification.ts

@@ -1,15 +1,18 @@
+import { BASE_URL } from '$env/static/private';
 import { sendMail } from './resend';
 
 export async function sendVerificationEmail(options: {
 	email: string;
-	verificationUrl: string;
+	token: string;
 }) {
+	const verificationUrl = `${BASE_URL}/api/auth/verify-email?token=${options.token}&callbackURL=/login`;
+
 	await sendMail({
 		to: options.email,
 		templateId: 'email-verification-email',
 		data: {
 			target_email_address: options.email,
-			verification_link: options.verificationUrl
+			verification_link: verificationUrl
 		}
 	});
 }