fix(admin): delete feedback alerts + informative block errors (issue #127)

- locations/categories GET pass req.query.error/success to views
- locations/categories EJS render dismissible error/success alerts (modeled on catalog.ejs)
- Delete errors include blocking counts + 'Remove X first' hints
- 🔒 lock hint on rows with linked categories/products/subcategories
- 18 new tests (adminDeleteFeedback.test.js); 48 total pass

src/admin/views/locations.ejs

@@ -1,3 +1,15 @@
+<% if (error) { %>
+<div class="alert alert-danger alert-dismissible fade show" role="alert">
+    <%= error %>
+    <button type="button" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>
+</div>
+<% } %>
+<% if (success) { %>
+<div class="alert alert-success alert-dismissible fade show" role="alert">
+    <%= success %>
+    <button type="button" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>
+</div>
+<% } %>
 <a href="/catalog" class="btn btn-sm btn-outline-secondary mb-2">« Back to Catalog</a>
 <div class="panel panel-icon mb-3">
     <div class="panel-hdr">
@@ -71,6 +83,9 @@
                                     <input type="hidden" name="_csrf" value="<%= csrfToken %>">
                                     <button class="btn btn-sm btn-danger">Delete</button>
                                 </form>
+                                <% if (l.category_count > 0 || l.product_count > 0) { %>
+                                <span class="text-warning" title="Blocks deletion">🔒</span>
+                                <% } %>
                             </td>
                         </tr>
                         <% }); %>