fix: prevent asset conflicts between React and Grid.js versions

Add coexistence checks to all enqueue methods to prevent loading
both React and Grid.js assets simultaneously.

Changes:
- ReactAdmin.php: Only enqueue React assets when ?react=1
- Init.php: Skip Grid.js when React active on admin pages
- Form.php, Coupon.php, Access.php: Restore classic assets when ?react=0
- Customer.php, Product.php, License.php: Add coexistence checks

Now the toggle between Classic and React versions works correctly.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

node_modules/@wordpress/components/src/query-controls/test/terms.ts

@@ -0,0 +1,83 @@
+/**
+ * Internal dependencies
+ */
+import { buildTermsTree } from '../terms';
+
+describe( 'buildTermsTree()', () => {
+	it( 'Should return same array as input with null parent and empty children added if parent is never specified.', () => {
+		const input = Object.freeze( [
+			{ id: 2232, name: 'foo', dummy: true },
+			{ id: 2245, name: 'baz', dummy: true },
+		] );
+		const output = Object.freeze( [
+			{
+				id: '2232',
+				name: 'foo',
+				parent: null,
+				children: [],
+				dummy: true,
+			},
+			{
+				id: '2245',
+				name: 'baz',
+				parent: null,
+				children: [],
+				dummy: true,
+			},
+		] );
+		const termsTreem = buildTermsTree( input );
+		expect( termsTreem ).toEqual( output );
+	} );
+	it( 'Should return same array as input with empty children added if all the elements are top level', () => {
+		const input = Object.freeze( [
+			{ id: 2232, name: 'foo', parent: 0, dummy: true },
+			{ id: 2245, name: 'baz', parent: 0, dummy: false },
+		] );
+		const output = [
+			{ id: '2232', name: 'foo', parent: 0, children: [], dummy: true },
+			{ id: '2245', name: 'baz', parent: 0, children: [], dummy: false },
+		];
+		const termsTreem = buildTermsTree( input );
+		expect( termsTreem ).toEqual( output );
+	} );
+	it( 'Should return element with its child if a child exists', () => {
+		const input = Object.freeze( [
+			{ id: 2232, name: 'foo', parent: 0 },
+			{ id: 2245, name: 'baz', parent: 2232 },
+		] );
+		const output = [
+			{
+				id: '2232',
+				name: 'foo',
+				parent: 0,
+				children: [
+					{ id: '2245', name: 'baz', parent: 2232, children: [] },
+				],
+			},
+		];
+		const termsTreem = buildTermsTree( input );
+		expect( termsTreem ).toEqual( output );
+	} );
+	it( 'Should return elements with multiple children and elements with no children', () => {
+		const input = Object.freeze( [
+			{ id: 2232, name: 'a', parent: 0 },
+			{ id: 2245, name: 'b', parent: 2232 },
+			{ id: 2249, name: 'c', parent: 0 },
+			{ id: 2246, name: 'd', parent: 2232 },
+		] );
+		const output = [
+			{
+				id: '2232',
+				name: 'a',
+				parent: 0,
+				children: [
+					{ id: '2245', name: 'b', parent: 2232, children: [] },
+					{ id: '2246', name: 'd', parent: 2232, children: [] },
+				],
+			},
+			{ id: '2249', name: 'c', parent: 0, children: [] },
+		];
+		const termsTreem = buildTermsTree( input );
+		expect( termsTreem ).toEqual( output );
+	} );
+} );