Enforce quarterly run limit on AI price check

- GET: sets ViewBag.NextRunAvailable if last run was within 90 days;
  view disables the button and shows the next eligible date
- POST: returns early with a warning if called before the 90-day window

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

src/PowderCoating.Web/Views/CatalogItems/AiPriceCheck.cshtml

@@ -94,14 +94,26 @@
     <a asp-action="Index" class="btn btn-outline-secondary btn-sm">
         <i class="bi bi-arrow-left me-1"></i> Back to Catalog
     </a>
-    <form asp-action="RunAiPriceCheck" method="post" id="runForm" class="run-btn-wrap">
-        @Html.AntiForgeryToken()
-        <button type="submit" class="btn btn-primary" id="runBtn"
-                data-item-count="@(ViewBag.ActiveItemCount ?? 0)">
-            <i class="bi bi-robot me-2"></i>
-            @(Model == null ? "Run Price Check" : "Re-run Price Check")
-        </button>
-    </form>
+    @if (ViewBag.NextRunAvailable != null)
+    {
+        <div class="text-end">
+            <button class="btn btn-primary" disabled>
+                <i class="bi bi-robot me-2"></i>Re-run Price Check
+            </button>
+            <div class="small text-muted mt-1">Next run available: @ViewBag.NextRunAvailable</div>
+        </div>
+    }
+    else
+    {
+        <form asp-action="RunAiPriceCheck" method="post" id="runForm" class="run-btn-wrap">
+            @Html.AntiForgeryToken()
+            <button type="submit" class="btn btn-primary" id="runBtn"
+                    data-item-count="@(ViewBag.ActiveItemCount ?? 0)">
+                <i class="bi bi-robot me-2"></i>
+                @(Model == null ? "Run Price Check" : "Re-run Price Check")
+            </button>
+        </form>
+    }
 </div>
 
 @if (TempData["Success"] != null)