fix(data-drains): mirror webhook signingSecret min length in form gate

isComplete now requires signingSecret >= 32 to match the contract/runtime
schema so the Save button can't enable on a value that will fail server-side.

Author: waleedlatif1

apps/sim/ee/data-drains/destinations/registry.tsx

@@ -485,7 +485,7 @@ const webhookFormSpec: DestinationFormSpec<WebhookState> = {
       </FormField>
     </>
   ),
-  isComplete: (s) => s.url.length > 0 && s.signingSecret.length >= 8,
+  isComplete: (s) => s.url.length > 0 && s.signingSecret.length >= 32,
   toDestinationBranch: (s) => ({
     destinationType: 'webhook',
     destinationConfig: {