Add PWA manifest, fix AI multi-coat pricing, and improve catalog lookup

- PWA: manifest.json + minimal service worker so iOS/Android persist camera
  permission after "Add to Home Screen"; theme-color and apple meta tags in layout
- PWA icons: 192x192 and 512x512 from transparent PCL logo; updated pcl-logo.png
- AI pricing: apply AdditionalCoatLaborPercent per extra coat on AI items,
  matching the calculated-item path (was ignoring extra coats entirely)
- AI wizard: live price recalc when coats are added/removed; session-expiry
  errors now show a clear "refresh and sign in" message instead of raw HTTP status;
  smooth-scroll to follow-up/results sections on AI response
- Catalog lookup: exclude SKUs already in company inventory from results;
  pass currentId on edit so own entry still appears; vendor-scoped search
  with cross-vendor fallback; result count shown in multi-match modal

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

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

@@ -101,6 +101,12 @@
     <meta charset="utf-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>@ViewData["Title"] - Powder Coating Logix</title>
+    <link rel="manifest" href="/manifest.json" />
+    <meta name="theme-color" content="#1A1A1C" />
+    <meta name="mobile-web-app-capable" content="yes" />
+    <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" />
 
     <!-- First-paint theme: server already stamped data-surface from cookie.
          This script only corrects first-visit (no cookie) using OS preference. -->
@@ -2192,5 +2198,10 @@
         }, true);
     })();
     </script>
+    <script>
+        if ('serviceWorker' in navigator) {
+            navigator.serviceWorker.register('/sw.js').catch(() => {});
+        }
+    </script>
 </body>
 </html>