fix(mcp-server): jarvis.marketplace.certify routes to wrong endpoint on rejection

The backend has two separate endpoints:
  POST /marketplace/admin/:id/approve
  POST /marketplace/admin/:id/reject

Previously jarvisMarketplaceCertify always called /approve regardless of
the decision field — rejections would silently approve listings.

Fix: derive action from decision.decision ('approved' → 'approve', else 'reject')
and use the correct endpoint path.

services/mcp-server/src/lib/jarvis-client.ts

@@ -194,8 +194,9 @@ export function jarvisMarketplaceCertify(
   decision: { decision: 'approved' | 'rejected'; notes?: string },
   opts: JarvisClientOptions
 ): Promise<unknown> {
+  const action = decision.decision === 'approved' ? 'approve' : 'reject';
   return jarvisFetch(
-    `/marketplace/admin/${listingId}/approve`,
+    `/marketplace/admin/${listingId}/${action}`,
     { method: 'POST', body: JSON.stringify(decision) },
     opts
   );