fix(mcp): revert optimistic oauthClientId to undefined to match McpServer type

The response contract preprocesses null → undefined, so McpServer.oauthClientId
is string | undefined. Using null broke type checking.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: waleedlatif1

apps/sim/hooks/queries/mcp.ts

@@ -273,9 +273,7 @@ export function useUpdateMcpServer() {
         const { oauthClientSecret: _omitSecret, oauthClientId, ...rest } = updates
         const safeUpdates: Partial<McpServer> = { ...rest }
         if (oauthClientId !== undefined) {
-          // Server normalizes empty string → null; mirror that to avoid UI flicker
-          // between optimistic apply and server response invalidation.
-          safeUpdates.oauthClientId = oauthClientId || null
+          safeUpdates.oauthClientId = oauthClientId || undefined
         }
         queryClient.setQueryData<McpServer[]>(
           mcpKeys.serversList(workspaceId),