feat: add footer with attribution and source link

- Create Footer component with author info and repo link
- Add footer to root layout (appears on all pages)
- Include dedication to Lilly & Diego 🐈 🐈‍⬛

components/footer.tsx

@@ -0,0 +1,25 @@
+export function Footer() {
+    return (
+        <footer className="mt-auto py-6 px-4 border-t bg-muted/30">
+            <div className="max-w-4xl mx-auto text-center text-sm text-muted-foreground">
+                Made with ❤️ and 🍷 for Lilly & Diego by{" "}
+                <a
+                    href="mailto:elpatron+csp@mailbox.org"
+                    className="hover:underline font-medium text-foreground"
+                >
+                    Markus F.J. Busche
+                </a>
+                .{" "}
+                Source @{" "}
+                <a
+                    href="https://gitea.elpatron.me/elpatron/cat-sitting-planner"
+                    target="_blank"
+                    rel="noopener noreferrer"
+                    className="hover:underline font-medium text-foreground"
+                >
+                    https://gitea.elpatron.me/elpatron/cat-sitting-planner
+                </a>
+            </div>
+        </footer>
+    )
+}