style: replace emoji heart with primary Heart icon and polish Valknar link

- Swap 💜 for a filled Lucide Heart icon in text-primary in both Footer and AppSidebar
- Style Valknar link with animated underline (decoration-primary on hover)
- Add sidebar footer with copyright, Heart, Valknar link, and GitFork source link
- Add author field to package.json

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/Footer.tsx

@@ -1,7 +1,7 @@
 'use client';
 
 import { motion } from 'framer-motion';
-import { GitFork } from 'lucide-react';
+import { GitFork, Heart } from 'lucide-react';
 
 export default function Footer() {
   const currentYear = new Date().getFullYear();
@@ -17,8 +17,18 @@ export default function Footer() {
           transition={{ duration: 0.6 }}
         >
           {/* Copyright */}
-          <p className="text-sm text-muted-foreground">
-            © {currentYear} Kit. Built with Next.js 16 & Tailwind CSS 4
+          <p className="text-sm text-muted-foreground flex items-center gap-1">
+            © {currentYear} Kit.
+            <Heart className="h-4 w-4 text-primary shrink-0" fill="currentColor" />
+                <a
+                  href="https://pivoine.art"
+                  target="_blank"
+                  rel="noopener noreferrer"
+                  title="Pivoine.Art"
+                  className="font-medium underline underline-offset-4 decoration-primary/0 hover:decoration-primary transition-all duration-300"
+                >
+                  Valknar
+                </a>
           </p>
 
           {/* Source link */}