feat: build React Form Builder (F2.7-F2.10)

Components:
- FieldPalette: drag-and-drop source for all field types
- FormCanvas: drop target with field list, reordering, CRUD
- FormField: individual field component with actions
- FieldSettingsPanel: edit field properties (label, ID, options, etc.)
- FormFieldOptions: manage select/radio/checkbox options
- FormPreview: live preview of rendered form
- FormFieldPreview: preview individual field types

Features:
- 16 field types (text, email, select, checkbox, radio, etc.)
- Categorized field palette
- Drag-and-drop field reordering
- Per-field settings panel
- Option management for choice fields
- Live form preview
- Save via AJAX

Config:
- fieldTypes.js: field definitions and constants
- Generate unique field IDs
- Field type categories (input, choice, layout, preset, advanced)

src/admin/pages/Forms.js

@@ -1,14 +1,32 @@
 /**
- * Forms Page - Placeholder
+ * Forms Page - List view and Form Builder
  */
 
 import { __ } from '@wordpress/i18n';
+import { useState } from '@wordpress/element';
+import FormBuilder from '../components/formBuilder/FormBuilder';
 
 export default function FormsPage({ initialData }) {
+    const [isBuilder, setIsBuilder] = useState(false);
+    const [selectedFormId, setSelectedFormId] = useState(null);
+
+    if (isBuilder) {
+        return (
+            <div className="formipay-page-forms">
+                <FormBuilder
+                    formId={selectedFormId}
+                    initialData={initialData}
+                />
+            </div>
+        );
+    }
+
     return (
-        <div className="formipay-page-formipay-page">
-            <h1>{ __('Forms', 'formipay') }</h1>
-            <p>{ __('Page content coming soon...', 'formipay') }</p>
+        <div className="formipay-page-forms">
+            <div className="formipay-forms-list">
+                <h1>{ __('Forms', 'formipay') }</h1>
+                <p>{ __('Forms list coming soon. Use the classic editor for now.', 'formipay') }</p>
+            </div>
         </div>
     );
 }