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/v8-to-istanbul/lib/function.js

@@ -0,0 +1,29 @@
+module.exports = class CovFunction {
+  constructor (name, startLine, startCol, endLine, endCol, count) {
+    this.name = name
+    this.startLine = startLine
+    this.startCol = startCol
+    this.endLine = endLine
+    this.endCol = endCol
+    this.count = count
+  }
+
+  toIstanbul () {
+    const loc = {
+      start: {
+        line: this.startLine,
+        column: this.startCol
+      },
+      end: {
+        line: this.endLine,
+        column: this.endCol
+      }
+    }
+    return {
+      name: this.name,
+      decl: loc,
+      loc,
+      line: this.startLine
+    }
+  }
+}