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/escape-html/src/escape-greater.js

@@ -0,0 +1,15 @@
+/**
+ * Returns a string with greater-than sign replaced.
+ *
+ * Note that if a resolution for Trac#45387 comes to fruition, it is no longer
+ * necessary for `__unstableEscapeGreaterThan` to exist.
+ *
+ * See: https://core.trac.wordpress.org/ticket/45387
+ *
+ * @param {string} value Original string.
+ *
+ * @return {string} Escaped string.
+ */
+export default function __unstableEscapeGreaterThan( value ) {
+	return value.replace( />/g, '>' );
+}

node_modules/@wordpress/escape-html/src/index.js

@@ -0,0 +1,123 @@
+/**
+ * Internal dependencies
+ */
+import __unstableEscapeGreaterThan from './escape-greater';
+
+/**
+ * Regular expression matching invalid attribute names.
+ *
+ * "Attribute names must consist of one or more characters other than controls,
+ * U+0020 SPACE, U+0022 ("), U+0027 ('), U+003E (>), U+002F (/), U+003D (=),
+ * and noncharacters."
+ *
+ * @see https://html.spec.whatwg.org/multipage/syntax.html#attributes-2
+ *
+ * @type {RegExp}
+ */
+const REGEXP_INVALID_ATTRIBUTE_NAME = /[\u007F-\u009F "'>/="\uFDD0-\uFDEF]/;
+
+/**
+ * Returns a string with ampersands escaped. Note that this is an imperfect
+ * implementation, where only ampersands which do not appear as a pattern of
+ * named, decimal, or hexadecimal character references are escaped. Invalid
+ * named references (i.e. ambiguous ampersand) are still permitted.
+ *
+ * @see https://w3c.github.io/html/syntax.html#character-references
+ * @see https://w3c.github.io/html/syntax.html#ambiguous-ampersand
+ * @see https://w3c.github.io/html/syntax.html#named-character-references
+ *
+ * @param {string} value Original string.
+ *
+ * @return {string} Escaped string.
+ */
+export function escapeAmpersand( value ) {
+	return value.replace( /&(?!([a-z0-9]+|#[0-9]+|#x[a-f0-9]+);)/gi, '&' );
+}
+
+/**
+ * Returns a string with quotation marks replaced.
+ *
+ * @param {string} value Original string.
+ *
+ * @return {string} Escaped string.
+ */
+export function escapeQuotationMark( value ) {
+	return value.replace( /"/g, '"' );
+}
+
+/**
+ * Returns a string with less-than sign replaced.
+ *
+ * @param {string} value Original string.
+ *
+ * @return {string} Escaped string.
+ */
+export function escapeLessThan( value ) {
+	return value.replace( /</g, '&lt;' );
+}
+
+/**
+ * Returns an escaped attribute value.
+ *
+ * @see https://w3c.github.io/html/syntax.html#elements-attributes
+ *
+ * "[...] the text cannot contain an ambiguous ampersand [...] must not contain
+ * any literal U+0022 QUOTATION MARK characters (")"
+ *
+ * Note we also escape the greater than symbol, as this is used by wptexturize to
+ * split HTML strings. This is a WordPress specific fix
+ *
+ * Note that if a resolution for Trac#45387 comes to fruition, it is no longer
+ * necessary for `__unstableEscapeGreaterThan` to be used.
+ *
+ * See: https://core.trac.wordpress.org/ticket/45387
+ *
+ * @param {string} value Attribute value.
+ *
+ * @return {string} Escaped attribute value.
+ */
+export function escapeAttribute( value ) {
+	return __unstableEscapeGreaterThan(
+		escapeQuotationMark( escapeAmpersand( value ) )
+	);
+}
+
+/**
+ * Returns an escaped HTML element value.
+ *
+ * @see https://w3c.github.io/html/syntax.html#writing-html-documents-elements
+ *
+ * "the text must not contain the character U+003C LESS-THAN SIGN (<) or an
+ * ambiguous ampersand."
+ *
+ * @param {string} value Element value.
+ *
+ * @return {string} Escaped HTML element value.
+ */
+export function escapeHTML( value ) {
+	return escapeLessThan( escapeAmpersand( value ) );
+}
+
+/**
+ * Returns an escaped Editable HTML element value. This is different from
+ * `escapeHTML`, because for editable HTML, ALL ampersands must be escaped in
+ * order to render the content correctly on the page.
+ *
+ * @param {string} value Element value.
+ *
+ * @return {string} Escaped HTML element value.
+ */
+export function escapeEditableHTML( value ) {
+	return escapeLessThan( value.replace( /&/g, '&amp;' ) );
+}
+
+/**
+ * Returns true if the given attribute name is valid, or false otherwise.
+ *
+ * @param {string} name Attribute name to test.
+ *
+ * @return {boolean} Whether attribute is valid.
+ */
+export function isValidAttributeName( name ) {
+	return ! REGEXP_INVALID_ATTRIBUTE_NAME.test( name );
+}

node_modules/@wordpress/escape-html/src/test/index.js

@@ -0,0 +1,113 @@
+/**
+ * Internal dependencies
+ */
+import {
+	escapeAmpersand,
+	escapeQuotationMark,
+	escapeLessThan,
+	escapeAttribute,
+	escapeHTML,
+	isValidAttributeName,
+	escapeEditableHTML,
+} from '../';
+import __unstableEscapeGreaterThan from '../escape-greater';
+
+function testUnstableEscapeGreaterThan( implementation ) {
+	it( 'should escape greater than', () => {
+		const result = implementation( 'Chicken > Ribs' );
+		expect( result ).toBe( 'Chicken > Ribs' );
+	} );
+}
+
+function testEscapeAmpersand( implementation ) {
+	it( 'should escape ampersand', () => {
+		const result = implementation(
+			'foo & bar & & baz Σ &#bad; Σ Σ &#xevil;'
+		);
+
+		expect( result ).toBe(
+			'foo & bar & & baz Σ &#bad; Σ Σ &#xevil;'
+		);
+	} );
+}
+
+function testEscapeQuotationMark( implementation ) {
+	it( 'should escape quotation mark', () => {
+		const result = implementation( '"Be gone!"' );
+
+		expect( result ).toBe( '"Be gone!"' );
+	} );
+}
+
+function testEscapeLessThan( implementation ) {
+	it( 'should escape less than', () => {
+		const result = implementation( 'Chicken < Ribs' );
+
+		expect( result ).toBe( 'Chicken &lt; Ribs' );
+	} );
+}
+
+describe( 'escapeAmpersand', () => {
+	testEscapeAmpersand( escapeAmpersand );
+} );
+
+describe( 'escapeQuotationMark', () => {
+	testEscapeQuotationMark( escapeQuotationMark );
+} );
+
+describe( 'escapeLessThan', () => {
+	testEscapeLessThan( escapeLessThan );
+} );
+
+describe( 'escapeGreaterThan', () => {
+	testUnstableEscapeGreaterThan( __unstableEscapeGreaterThan );
+} );
+
+describe( 'escapeAttribute', () => {
+	testEscapeAmpersand( escapeAttribute );
+	testEscapeQuotationMark( escapeAttribute );
+	testUnstableEscapeGreaterThan( escapeAttribute );
+} );
+
+describe( 'escapeHTML', () => {
+	testEscapeAmpersand( escapeHTML );
+	testEscapeLessThan( escapeHTML );
+} );
+
+describe( 'isValidAttributeName', () => {
+	it( 'should return false for attribute with controls', () => {
+		const result = isValidAttributeName( 'bad\u007F' );
+
+		expect( result ).toBe( false );
+	} );
+
+	it( 'should return false for attribute with non-permitted characters', () => {
+		const result = isValidAttributeName( 'bad"' );
+
+		expect( result ).toBe( false );
+	} );
+
+	it( 'should return false for attribute with noncharacters', () => {
+		const result = isValidAttributeName( 'bad\uFDD0' );
+
+		expect( result ).toBe( false );
+	} );
+
+	it( 'should return true for valid attribute name', () => {
+		const result = isValidAttributeName( 'good' );
+
+		expect( result ).toBe( true );
+	} );
+} );
+
+describe( 'escapeEditableHTML', () => {
+	it( 'should escape < and all ampersands', () => {
+		const result = escapeEditableHTML(
+			'<a href="https://w.org">WP</a> & &lt;strong&gt;'
+		);
+
+		expect( result ).toBe(
+			'&lt;a href="https://w.org">WP&lt;/a> &amp; &amp;lt;strong&amp;gt;'
+		);
+	} );
+} );