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>

types/qrcode.ts

@@ -0,0 +1,12 @@
+export type ErrorCorrectionLevel = 'L' | 'M' | 'Q' | 'H';
+
+export type ExportSize = 256 | 512 | 1024 | 2048;
+
+export interface QRCodeOptions {
+  text: string;
+  errorCorrection: ErrorCorrectionLevel;
+  foregroundColor: string;
+  backgroundColor: string;
+  margin: number;
+  size: ExportSize;
+}