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/fastq/bench.js

@@ -0,0 +1,66 @@
+'use strict'
+
+const max = 1000000
+const fastqueue = require('./')(worker, 1)
+const { promisify } = require('util')
+const immediate = promisify(setImmediate)
+const qPromise = require('./').promise(immediate, 1)
+const async = require('async')
+const neo = require('neo-async')
+const asyncqueue = async.queue(worker, 1)
+const neoqueue = neo.queue(worker, 1)
+
+function bench (func, done) {
+  const key = max + '*' + func.name
+  let count = -1
+
+  console.time(key)
+  end()
+
+  function end () {
+    if (++count < max) {
+      func(end)
+    } else {
+      console.timeEnd(key)
+      if (done) {
+        done()
+      }
+    }
+  }
+}
+
+function benchFastQ (done) {
+  fastqueue.push(42, done)
+}
+
+function benchAsyncQueue (done) {
+  asyncqueue.push(42, done)
+}
+
+function benchNeoQueue (done) {
+  neoqueue.push(42, done)
+}
+
+function worker (arg, cb) {
+  setImmediate(cb)
+}
+
+function benchSetImmediate (cb) {
+  worker(42, cb)
+}
+
+function benchFastQPromise (done) {
+  qPromise.push(42).then(function () { done() }, done)
+}
+
+function runBench (done) {
+  async.eachSeries([
+    benchSetImmediate,
+    benchFastQ,
+    benchNeoQueue,
+    benchAsyncQueue,
+    benchFastQPromise
+  ], bench, done)
+}
+
+runBench(runBench)