Task #10: Send automatic confirmation email to contact form submitters

After a visitor submits the contact form, Brevo now sends two emails:
1. The existing notification to jh@unixweb.de with the message details
2. A new confirmation email to the sender's address

The confirmation email:
- Is sent from "Joachim Hummel <jh@unixweb.de>"
- Addresses the sender by name
- Thanks them and sets response-time expectations (1-2 Werktage)
- Includes both plain-text and HTML versions
- Is logged separately via req.log.info for observability

If either email fails, the entire request returns a 500 error (atomic
behavior — both succeed or neither does from the user's perspective).

File changed:
- artifacts/api-server/src/routes/contact.ts

Also ran `pnpm --filter @workspace/api-spec run codegen` to fix a
pre-existing typecheck failure caused by stale generated lib output.
Typecheck passes cleanly after codegen.

Replit-Task-Id: a5d51157-6bd1-48c7-ba04-68e7d951eeab

artifacts/api-server/src/routes/contact.ts

@@ -50,6 +50,27 @@ router.post("/contact", async (req, res) => {
     });
 
     req.log.info({ to: "jh@unixweb.de", from: email }, "Contact message sent via Brevo");
+
+    await brevo.transactionalEmails.sendTransacEmail({
+      sender: { name: "Joachim Hummel", email: "jh@unixweb.de" },
+      to: [{ email, name }],
+      subject: "Ihre Anfrage ist angekommen – vielen Dank!",
+      textContent: [
+        `Hallo ${name},`,
+        "",
+        "vielen Dank für Ihre Nachricht! Ich habe Ihre Anfrage erhalten und melde mich in der Regel innerhalb von 1–2 Werktagen bei Ihnen.",
+        "",
+        "Mit freundlichen Grüßen",
+        "Joachim Hummel",
+      ].join("\n"),
+      htmlContent: `
+        <p>Hallo ${escapeHtml(name)},</p>
+        <p>vielen Dank für Ihre Nachricht! Ich habe Ihre Anfrage erhalten und melde mich in der Regel innerhalb von <strong>1–2 Werktagen</strong> bei Ihnen.</p>
+        <p>Mit freundlichen Grüßen<br />Joachim Hummel</p>
+      `,
+    });
+
+    req.log.info({ to: email }, "Confirmation email sent to sender via Brevo");
     res.json({ success: true, message: "Ihre Nachricht wurde erfolgreich gesendet." });
   } catch (err) {
     req.log.error({ err }, "Failed to send contact email via Brevo");