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/bare-os/lib/constants.js

@@ -0,0 +1,7 @@
+const binding = require('../binding')
+
+module.exports = {
+  signals: binding.signals,
+  errnos: binding.errnos,
+  priority: binding.priority
+}

node_modules/bare-os/lib/errors.js

@@ -0,0 +1,22 @@
+module.exports = class OSError extends Error {
+  constructor(msg, code, fn = OSError) {
+    super(`${code}: ${msg}`)
+    this.code = code
+
+    if (Error.captureStackTrace) {
+      Error.captureStackTrace(this, fn)
+    }
+  }
+
+  get name() {
+    return 'OSError'
+  }
+
+  static UNKNOWN_SIGNAL(msg) {
+    return new OSError(msg, 'UNKNOWN_SIGNAL', OSError.UNKNOWN_SIGNAL)
+  }
+
+  static TITLE_OVERFLOW(msg) {
+    return new OSError(msg, 'TITLE_OVERFLOW', OSError.TITLE_OVERFLOW)
+  }
+}