fix(contact): send the contact form through the mail service's /v1/send/message

POST /api/contact posted { to, subject, body, replyTo } to ${mailApiUrl}/send,
which the mail service (libreshop/mail src/app.py) does not have, so every
message failed with a 500. It now posts { to_email, subject, message } to
POST /v1/send/message, still to paperwork@muellerprints.de, with the same
subject and text as before. The service sets no Reply-To; the sender's
address stays in the text. A line break in the subject is replaced by a
space, so it cannot start another mail header.

mailApiUrl was read from runtimeConfig without being declared there, so
NUXT_MAIL_API_URL could not set it and the fallback http://mail:2222 was
always used. It is declared now, with that default; mp's compose.yml sets
no NUXT_MAIL_API_URL.

contactMail and mailSendUrl (server/utils/contactMail.ts) are pure and tested.

Refs libretech/mp#71

server/api/contact.post.ts

@@ -1,55 +1,18 @@
+import { contactMail, mailSendUrl } from "~/server/utils/contactMail";
+
 export default defineEventHandler(async (event) => {
-	const body = await readBody(event);
-
-	const { name, email, subject, message } = body;
-
-	if (!name || !email || !message) {
-		throw createError({
-			statusCode: 400,
-			message: "Name, E-Mail und Nachricht sind erforderlich",
-		});
-	}
-
-	// Validate email format
-	const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
-	if (!emailRegex.test(email)) {
-		throw createError({
-			statusCode: 400,
-			message: "Ungültige E-Mail-Adresse",
-		});
+	const result = contactMail(await readBody(event));
+	if (result.ok === false) {
+		throw createError({ statusCode: 400, message: result.message });
 	}
 
 	try {
-		// Send email via Mail service
 		const config = useRuntimeConfig();
-		const mailApiUrl = config.mailApiUrl || "http://mail:2222";
-
-		await $fetch(`${mailApiUrl}/send`, {
-			method: "POST",
-			body: {
-				to: "paperwork@muellerprints.de",
-				subject: `Kontaktanfrage: ${subject || "Anfrage über Website"}`,
-				body: `
-Name: ${name}
-E-Mail: ${email}
-Betreff: ${subject || "Kontaktanfrage über Website"}
-
-Nachricht:
-${message}
-
----
-Diese Nachricht wurde über das Kontaktformular auf muellerprints.de gesendet.
-				`.trim(),
-				replyTo: email,
-			},
-		});
+		await $fetch(mailSendUrl(config.mailApiUrl || "http://mail:2222"), { method: "POST", body: result.mail });
 
 		return { success: true };
 	} catch (error) {
 		console.error("Failed to send contact email:", error);
-		throw createError({
-			statusCode: 500,
-			message: "E-Mail konnte nicht gesendet werden",
-		});
+		throw createError({ statusCode: 500, message: "E-Mail konnte nicht gesendet werden" });
 	}
 });