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/indent-string/index.d.ts

@@ -0,0 +1,42 @@
+declare namespace indentString {
+	interface Options {
+		/**
+		The string to use for the indent.
+
+		@default ' '
+		*/
+		readonly indent?: string;
+
+		/**
+		Also indent empty lines.
+
+		@default false
+		*/
+		readonly includeEmptyLines?: boolean;
+	}
+}
+
+/**
+Indent each line in a string.
+
+@param string - The string to indent.
+@param count - How many times you want `options.indent` repeated. Default: `1`.
+
+@example
+```
+import indentString = require('indent-string');
+
+indentString('Unicorns\nRainbows', 4);
+//=> '    Unicorns\n    Rainbows'
+
+indentString('Unicorns\nRainbows', 4, {indent: '♥'});
+//=> '♥♥♥♥Unicorns\n♥♥♥♥Rainbows'
+```
+*/
+declare function indentString(
+	string: string,
+	count?: number,
+	options?: indentString.Options
+): string;
+
+export = indentString;