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/json2php/src/json2php.coffee

@@ -0,0 +1,42 @@
+make = ({linebreak = '', indent = '', shortArraySyntax = false} = {}) ->
+  arrOpen = if shortArraySyntax then '[' else 'array('
+  arrClose = if shortArraySyntax then ']' else ')'
+  nest = {
+    '[object Array]': (obj, parentIndent) ->
+      for value in obj
+        transform(value, parentIndent)
+
+    '[object Object]': (obj, parentIndent) ->
+      for own key, value of obj
+        transform(key, parentIndent) + ' => ' + transform(value, parentIndent)
+  }
+
+  transform = (obj, parentIndent = '') ->
+    objType = Object.prototype.toString.call(obj)
+    switch objType
+      when '[object Null]', '[object Undefined]'
+        result = 'null'
+      when '[object String]'
+        result = "'" + obj.replace(///\\///g, '\\\\').replace(///\'///g, "\\'") + "'"
+      when '[object Number]', '[object Boolean]'
+        result = obj.toString()
+      when '[object Array]', '[object Object]'
+        nestIndent = parentIndent + indent
+        items = nest[objType](obj, nestIndent)
+        result = """
+          #{arrOpen}#{linebreak + nestIndent}#{
+            items.join(',' + if linebreak == '' then ' ' else linebreak + nestIndent)
+          }#{linebreak + parentIndent}#{arrClose}
+        """
+      else
+        result = 'null'
+    result
+
+json2php = make()
+
+json2php.make = make
+
+if typeof module isnt 'undefined' and module.exports
+  module.exports = json2php
+  # Not that good but useful
+  global.json2php = json2php