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/v8-to-istanbul/lib/line.js

@@ -0,0 +1,34 @@
+module.exports = class CovLine {
+  constructor (line, startCol, lineStr) {
+    this.line = line
+    // note that startCol and endCol are absolute positions
+    // within a file, not relative to the line.
+    this.startCol = startCol
+
+    // the line length itself does not include the newline characters,
+    // these are however taken into account when enumerating absolute offset.
+    const matchedNewLineChar = lineStr.match(/\r?\n$/u)
+    const newLineLength = matchedNewLineChar ? matchedNewLineChar[0].length : 0
+    this.endCol = startCol + lineStr.length - newLineLength
+
+    // we start with all lines having been executed, and work
+    // backwards zeroing out lines based on V8 output.
+    this.count = 1
+
+    // set by source.js during parsing, if /* c8 ignore next */ is found.
+    this.ignore = false
+  }
+
+  toIstanbul () {
+    return {
+      start: {
+        line: this.line,
+        column: 0
+      },
+      end: {
+        line: this.line,
+        column: this.endCol - this.startCol
+      }
+    }
+  }
+}