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>

lib/qrcode/qrcodeService.ts

@@ -0,0 +1,39 @@
+import QRCode from 'qrcode';
+import type { ErrorCorrectionLevel } from '@/types/qrcode';
+
+export async function generateSvg(
+  text: string,
+  errorCorrection: ErrorCorrectionLevel,
+  foregroundColor: string,
+  backgroundColor: string,
+  margin: number,
+): Promise<string> {
+  return QRCode.toString(text, {
+    type: 'svg',
+    errorCorrectionLevel: errorCorrection,
+    color: {
+      dark: foregroundColor,
+      light: backgroundColor,
+    },
+    margin,
+  });
+}
+
+export async function generateDataUrl(
+  text: string,
+  errorCorrection: ErrorCorrectionLevel,
+  foregroundColor: string,
+  backgroundColor: string,
+  margin: number,
+  size: number,
+): Promise<string> {
+  return QRCode.toDataURL(text, {
+    errorCorrectionLevel: errorCorrection,
+    color: {
+      dark: foregroundColor,
+      light: backgroundColor,
+    },
+    margin,
+    width: size,
+  });
+}