Button consistency sweep + mobile responsiveness patches

- Standardize modal dismiss/cancel buttons to btn-outline-secondary across 70+ views
- Remove btn-sm from page-level Create and Back buttons (Index + Detail pages)
- Fix Edit buttons on Details pages: btn-secondary -> btn-warning
- Fix form Cancel/Back links: btn-secondary -> btn-outline-secondary
- Add 10 CSS patches to site.css for mobile/tablet responsiveness:
  top-navbar overflow prevention, page-header flex-wrap at 575px,
  table action button min-height override, notification dropdown width cap,
  tablet content padding

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

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

@@ -91,7 +91,7 @@
 </div>
 
 <div class="d-flex justify-content-between align-items-center mb-4">
-    <a asp-action="Index" class="btn btn-outline-secondary btn-sm">
+    <a asp-action="Index" class="btn btn-outline-secondary">
         <i class="bi bi-arrow-left me-1"></i> Back to Catalog
     </a>
     @if (!(bool)(ViewBag.AiPriceCheckEnabled ?? true))

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

@@ -215,7 +215,7 @@
                 <div id="categoryModalError" class="alert alert-danger d-none"></div>
             </div>
             <div class="modal-footer">
-                <button type="button" class="btn btn-secondary" data-bs-dismiss="modal">Cancel</button>
+                <button type="button" class="btn btn-outline-secondary" data-bs-dismiss="modal">Cancel</button>
                 <button type="button" class="btn btn-primary" id="saveCategoryBtn">
                     <i class="bi bi-check-circle me-1"></i>Create Category
                 </button>

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

@@ -238,7 +238,7 @@
                 <div id="categoryModalError" class="alert alert-danger d-none"></div>
             </div>
             <div class="modal-footer">
-                <button type="button" class="btn btn-secondary" data-bs-dismiss="modal">Cancel</button>
+                <button type="button" class="btn btn-outline-secondary" data-bs-dismiss="modal">Cancel</button>
                 <button type="button" class="btn btn-primary" id="saveCategoryBtn">
                     <i class="bi bi-check-circle me-1"></i>Create Category
                 </button>