Add platform powder catalog, catalog-first lookup, and label scanner

- Platform PowderCatalogItem table (IPlainRepository, no tenant filter) with
  full spec fields: cure temp/time, finish, color families, clear coat flag,
  coverage sq ft/lb, transfer efficiency, IsUserContributed
- Two EF migrations: AddPowderCatalogItem + AddPowderCatalogSpecFields
- PowderCatalogController (SuperAdminOnly): import from Prismatic JSON scrape,
  Lookup AJAX endpoint (catalog-first, ranked by SKU exact match), stats view
  with Tenant Contributed card
- Unified smart Lookup button on inventory Create/Edit: catalog hit fills all
  fields via catalogSnapshot pattern; AI augments cure/finish data from product
  URL if subscription enabled; catalog miss falls through to AI lookup
- In-browser label scanner (_LabelScanModal): getUserMedia live camera feed,
  jsQR auto-detects QR codes in rAF loop; "Scan Label Text" fallback sends
  captured frame to Claude vision via /Inventory/ScanLabel
- ScanLabel endpoint handles both QR URL path (LookupByUrlAsync) and vision
  path (ScanLabelAsync); auto-inserts unrecognized products as
  IsUserContributed=true; returns wasInCatalog/addedToCatalog flags

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

src/PowderCoating.Web/Views/Inventory/Details.cshtml

@@ -190,6 +190,26 @@
                                         </p>
                                     </div>
                                 }
+                                @if (!string.IsNullOrEmpty(Model.SdsUrl) || !string.IsNullOrEmpty(Model.TdsUrl))
+                                {
+                                    <div class="col-12">
+                                        <label class="text-muted small mb-1">Data Sheets</label>
+                                        <div class="d-flex gap-2 flex-wrap">
+                                            @if (!string.IsNullOrEmpty(Model.SdsUrl))
+                                            {
+                                                <a href="@Model.SdsUrl" target="_blank" class="btn btn-sm btn-outline-secondary">
+                                                    <i class="bi bi-file-earmark-pdf me-1"></i>Safety Data Sheet
+                                                </a>
+                                            }
+                                            @if (!string.IsNullOrEmpty(Model.TdsUrl))
+                                            {
+                                                <a href="@Model.TdsUrl" target="_blank" class="btn btn-sm btn-outline-secondary">
+                                                    <i class="bi bi-file-earmark-text me-1"></i>Technical Data Sheet
+                                                </a>
+                                            }
+                                        </div>
+                                    </div>
+                                }
                             }
                             @if (!string.IsNullOrEmpty(Model.Notes))
                             {