Offer a new share as a QR code and through the share sheet

The share created page gets "Show QR code", a dialog with the link as a
QR code (black on white, full screen on a phone) that downloads as a PNG
drawn in the browser, with a password reminder for protected shares; and
"Share…", which opens the device's share sheet where there is one. Both
carry only the link.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V9NnLxnPp8vaaurb3Z1MFy

app/Services/QrCodeService.php

@@ -0,0 +1,37 @@
+<?php
+
+namespace App\Services;
+
+use BaconQrCode\Common\ErrorCorrectionLevel;
+use BaconQrCode\Encoder\Encoder;
+use BaconQrCode\Renderer\Color\Rgb;
+use BaconQrCode\Renderer\Image\SvgImageBackEnd;
+use BaconQrCode\Renderer\ImageRenderer;
+use BaconQrCode\Renderer\RendererStyle\Fill;
+use BaconQrCode\Renderer\RendererStyle\RendererStyle;
+use BaconQrCode\Writer;
+
+class QrCodeService
+{
+    /**
+     * The QR code's width and height in the SVG, in pixels: the size a canvas draws it at.
+     */
+    public const SIZE = 1024;
+
+    /**
+     * Draw the contents as a QR code in SVG: black on white with a four-module quiet zone and
+     * error correction M, the most reliable to scan from a screen or a print. The XML declaration
+     * is dropped so the markup can sit inline in a page.
+     */
+    public function svg(string $contents): string
+    {
+        $svg = (new Writer(
+            new ImageRenderer(
+                new RendererStyle(self::SIZE, 4, null, null, Fill::uniformColor(new Rgb(255, 255, 255), new Rgb(0, 0, 0))),
+                new SvgImageBackEnd,
+            ),
+        ))->writeString($contents, Encoder::DEFAULT_BYTE_MODE_ENCODING, ErrorCorrectionLevel::M());
+
+        return trim(substr($svg, strpos($svg, "\n") + 1));
+    }
+}