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/minimalistic-assert/LICENSE

@@ -0,0 +1,13 @@
+Copyright 2015 Calvin Metcalf
+
+Permission to use, copy, modify, and/or distribute this software for any purpose
+with or without fee is hereby granted, provided that the above copyright notice
+and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
+OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+PERFORMANCE OF THIS SOFTWARE.

node_modules/minimalistic-assert/index.js

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+module.exports = assert;
+
+function assert(val, msg) {
+  if (!val)
+    throw new Error(msg || 'Assertion failed');
+}
+
+assert.equal = function assertEqual(l, r, msg) {
+  if (l != r)
+    throw new Error(msg || ('Assertion failed: ' + l + ' != ' + r));
+};

node_modules/minimalistic-assert/package.json

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+{
+  "name": "minimalistic-assert",
+  "version": "1.0.1",
+  "description": "minimalistic-assert ===",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/calvinmetcalf/minimalistic-assert.git"
+  },
+  "author": "",
+  "license": "ISC",
+  "bugs": {
+    "url": "https://github.com/calvinmetcalf/minimalistic-assert/issues"
+  },
+  "homepage": "https://github.com/calvinmetcalf/minimalistic-assert"
+}

node_modules/minimalistic-assert/readme.md

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+minimalistic-assert
+===
+
+very minimalistic assert module.