feat: add comprehensive loading feedback (#18)

frontend/src/app/components/apartment-form/apartment-form.css

@@ -27,6 +27,17 @@
   background: var(--surface);
   box-shadow: 0 1px 0 rgba(255, 255, 255, 0.04);
 }
+fieldset {
+  min-width: 0;
+  margin: 0;
+  padding: 0;
+  border: 0;
+}
+.primary-action mat-spinner {
+  display: inline-block;
+  margin-right: 8px;
+  vertical-align: middle;
+}
 .form-grid {
   display: grid;
   grid-template-columns: minmax(0, 1fr);