PR 4: Production guardrails for Seed Data and Storage Migration

- SeedData/Index: added prominent danger banner when running in Production (environment include="Production") so operators are clearly warned before writing to the live database; page remains accessible since seeding is occasionally valid in prod for new company onboarding
- StorageMigration/Index: added warning banner in Production explaining the tool is not needed now that Azure Blob migration is complete
- PlatformAdminController: hide Storage Migration hub card in Production via ShowStorageMigration flag (same WEBSITE_SITE_NAME pattern as ShowRawLogFiles); Seed Data card remains visible so prod onboarding stays reachable

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

src/PowderCoating.Web/Views/SeedData/Index.cshtml

@@ -24,6 +24,16 @@
         </a>
     </div>
 
+    <environment include="Production">
+    <div class="alert alert-danger alert-permanent d-flex gap-3 align-items-start mb-4">
+        <i class="bi bi-exclamation-octagon-fill fs-4 flex-shrink-0 mt-1 text-danger"></i>
+        <div>
+            <div class="fw-semibold">You are running in Production</div>
+            <div class="small mt-1">Seed operations write data directly to the live database. Only proceed if you have a specific, intentional reason — for example, onboarding a new company. Do not seed the default demo company in production.</div>
+        </div>
+    </div>
+    </environment>
+
     @if (TempData["SuccessMessage"] != null)
     {
         <div class="alert alert-success alert-dismissible alert-permanent fade show" role="alert">