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/whatwg-encoding/lib/supported-names.json

@@ -0,0 +1,37 @@
+[
+  "UTF-8",
+  "IBM866",
+  "ISO-8859-2",
+  "ISO-8859-3",
+  "ISO-8859-4",
+  "ISO-8859-5",
+  "ISO-8859-6",
+  "ISO-8859-7",
+  "ISO-8859-8",
+  "ISO-8859-10",
+  "ISO-8859-13",
+  "ISO-8859-14",
+  "ISO-8859-15",
+  "ISO-8859-16",
+  "KOI8-R",
+  "KOI8-U",
+  "macintosh",
+  "windows-874",
+  "windows-1250",
+  "windows-1251",
+  "windows-1252",
+  "windows-1253",
+  "windows-1254",
+  "windows-1255",
+  "windows-1256",
+  "windows-1257",
+  "windows-1258",
+  "GBK",
+  "gb18030",
+  "Big5",
+  "EUC-JP",
+  "Shift_JIS",
+  "EUC-KR",
+  "UTF-16BE",
+  "UTF-16LE"
+]