Add collapsible band editor to grid components

Introduce a toggleable "Band-Layout konfigurieren" section in CatalogsGrid.razor and MassDataGrid.razor, allowing users to expand or collapse the band editor UI. Added bandEditorExpanded state to control visibility. Updated CSS to style the new toggle button and its expanded/collapsed states, improving usability and reducing UI clutter.

DbFirst.BlazorWebApp/wwwroot/app.css

@@ -11,6 +11,7 @@ html, body {
 .app-light {
     --band-editor-bg: #f8f9fa;
     --band-editor-border: #dee2e6;
+    --band-toggle-hover-bg: #e9ecef;
 }
 
 .app-dark {
@@ -18,6 +19,7 @@ html, body {
     color: #f1f1f1;
     --band-editor-bg: #2d2d2d;
     --band-editor-border: #444444;
+    --band-toggle-hover-bg: #3a3a3a;
 }
 
 a, .btn-link {
@@ -74,15 +76,47 @@ h1:focus {
 
 /* Grid Band-Editor */
 .band-editor {
-    display: flex;
-    flex-direction: column;
-    gap: 12px;
-    padding: 12px;
     margin-top: 4px;
     margin-bottom: 16px;
     border: 1px solid var(--band-editor-border);
     border-radius: 4px;
     background-color: var(--band-editor-bg);
+    overflow: hidden;
+}
+
+.band-editor-toggle {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+    width: 100%;
+    padding: 8px 12px;
+    background: none;
+    border: none;
+    cursor: pointer;
+    font-size: inherit;
+    color: inherit;
+    text-align: left;
+}
+
+    .band-editor-toggle:hover {
+        background-color: var(--band-toggle-hover-bg);
+    }
+
+.band-editor-toggle-icon {
+    font-size: 0.7rem;
+    transition: transform 0.2s ease;
+    display: inline-block;
+}
+
+    .band-editor-toggle-icon.expanded {
+        transform: rotate(90deg);
+    }
+
+.band-editor-body {
+    display: flex;
+    flex-direction: column;
+    gap: 12px;
+    padding: 0 12px 12px 12px;
 }
 
 .band-controls {