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/StorageMigration/Index.cshtml

@@ -12,6 +12,16 @@
         </a>
     </div>
 
+    <environment include="Production">
+    <div class="alert alert-warning alert-permanent d-flex gap-3 align-items-start mb-4">
+        <i class="bi bi-exclamation-triangle-fill fs-4 flex-shrink-0 mt-1"></i>
+        <div>
+            <div class="fw-semibold">This tool is not needed in Production</div>
+            <div class="small mt-1">The platform has already migrated to Azure Blob Storage. Running this migration again in production is unnecessary and may cause unintended side effects. If you believe there is a specific reason to proceed, verify with the team first.</div>
+        </div>
+    </div>
+    </environment>
+
     <div class="row g-4">
         <!-- Status Card -->
         <div class="col-md-6">