add SettingsField struct and repeater field type for block settings

Introduces typed settings schema with SettingsField struct, replaces
the read-only JSON textarea with a full repeater UI for info_card items.
Supports add, remove, reorder and inline editing of repeater items.

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

assets/css/admin/components.css

@@ -1346,16 +1346,55 @@
   gap: 0.625rem;
 }
 
-.block-settings-json {
-  font-family: ui-monospace, "SF Mono", "Cascadia Mono", Menlo, monospace;
-  font-size: 0.75rem;
-  opacity: 0.7;
+/* Repeater fields */
+
+.repeater-field {
+  display: flex;
+  flex-direction: column;
+  gap: 0.5rem;
 }
 
-.block-settings-hint {
-  font-size: 0.75rem;
-  color: color-mix(in oklch, var(--t-text-primary) 50%, transparent);
-  margin-top: 0.25rem;
+.repeater-items {
+  list-style: none;
+  padding: 0;
+  margin: 0;
+  display: flex;
+  flex-direction: column;
+  gap: 0.5rem;
+}
+
+.repeater-item {
+  border: 1px solid var(--t-border-default);
+  border-radius: 0.375rem;
+  padding: 0.5rem;
+
+  & fieldset {
+    border: none;
+    padding: 0;
+    margin: 0;
+  }
+}
+
+.repeater-item-fields {
+  display: flex;
+  flex-direction: column;
+  gap: 0.375rem;
+}
+
+.repeater-item-controls {
+  display: flex;
+  gap: 0.125rem;
+  justify-content: flex-end;
+  margin-top: 0.375rem;
+}
+
+.repeater-remove-btn {
+  color: var(--t-danger);
+}
+
+.repeater-add-btn {
+  align-self: flex-start;
+  border-style: dashed;
 }
 
 } /* @layer admin */