feat: enhance webhook security with configurable allow list (#719)

- Add enableAllowList flag to webhook settings for flexible access control
- Update frontend UI with toggle switch and improved user experience
- Maintain backward compatibility with default allow-all behavior
- Add input validation hints and better form controls across admin panels

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <noreply@anthropic.com>

worker/src/models/index.ts

@@ -14,9 +14,11 @@ export type Passkey = {
 };
 
 export class AdminWebhookSettings {
+    enableAllowList: boolean;
     allowList: string[];
 
-    constructor(allowList: string[]) {
+    constructor(enableAllowList: boolean, allowList: string[]) {
+        this.enableAllowList = enableAllowList;
         this.allowList = allowList;
     }
 }