feat: add QR code generator tool

Add a sixth tool with live SVG preview, customizable foreground/background
colors, error correction level, margin control, and export as PNG (256–2048px)
or SVG. URL params enable shareable state. All processing runs client-side
via the qrcode package.

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

app/(app)/qrcode/page.tsx

@@ -0,0 +1,19 @@
+import type { Metadata } from 'next';
+import { QRCodeGenerator } from '@/components/qrcode/QRCodeGenerator';
+import { AppPage } from '@/components/layout/AppPage';
+import { getToolByHref } from '@/lib/tools';
+
+const tool = getToolByHref('/qrcode')!;
+
+export const metadata: Metadata = { title: tool.title };
+
+export default function QRCodePage() {
+  return (
+    <AppPage
+      title={tool.title}
+      description={tool.description}
+    >
+      <QRCodeGenerator />
+    </AppPage>
+  );
+}