Fix iOS PWA icon: add apple-touch-icon with white background

iOS ignores manifest icons for home screen; requires apple-touch-icon link tag.
Generated 180x180 PNG with white background + padding so the transparent logo
renders correctly instead of filling black.

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

src/PowderCoating.Web/Views/Shared/_Layout.cshtml

@@ -107,6 +107,7 @@
     <meta name="apple-mobile-web-app-capable" content="yes" />
     <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
     <meta name="apple-mobile-web-app-title" content="PCLogix" />
+    <link rel="apple-touch-icon" sizes="180x180" href="/images/apple-touch-icon.png" />
 
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