feat: Add UI to manage web widget allowed domains (#12495)

## Summary
- add allowed domains controls in the web widget configuration page.

<img width="1064" height="699" alt="Screenshot 2025-09-23 at 8 52 21 PM"
src="https://github.com/user-attachments/assets/8afd60b6-c81d-4f52-9cbe-07e70ad003d2"
/>


fixes:
https://linear.app/chatwoot/issue/CW-5661/add-the-options-for-configure-allowed-domains-for-web-widget

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>
Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>
Co-authored-by: iamsivin <iamsivin@gmail.com>

app/javascript/dashboard/helper/URLHelper.js

@@ -145,3 +145,34 @@ export const extractFilenameFromUrl = url => {
     return match ? match[1] : url;
   }
 };
+
+/**
+ * Normalizes a comma/newline separated list of domains
+ * @param {string} domains - The comma/newline separated list of domains
+ * @returns {string} - The normalized list of domains
+ * - Converts newlines to commas
+ * - Trims whitespace
+ * - Lowercases entries
+ * - Removes empty values
+ * - De-duplicates while preserving original order
+ */
+export const sanitizeAllowedDomains = domains => {
+  if (!domains) return '';
+
+  const tokens = domains
+    .replace(/\r\n/g, '\n')
+    .replace(/\s*\n\s*/g, ',')
+    .split(',')
+    .map(d => d.trim().toLowerCase())
+    .filter(d => d.length > 0);
+
+  // De-duplicate while preserving order using Set and filter index
+  const seen = new Set();
+  const unique = tokens.filter(d => {
+    if (seen.has(d)) return false;
+    seen.add(d);
+    return true;
+  });
+
+  return unique.join(',');
+};