fix: address code review findings (C1, I1, I2)

- C1: Include 'unreachable' peers in queueOutboxEvent query to prevent
  UNIQUE constraint violation when creating placeholders
- I1: Add 'rejected' to StatusFilter in FederationPanel so admins can
  see and manage rejected peers with delete/re-initiate actions
- I2: Map ensurePeered 'failed' to 'pending' in peer/ensure response
  to match spec and client expectations

packages/server/src/routes/federation.ts

@@ -517,9 +517,9 @@ export async function federationRoutes(app: FastifyInstance): Promise<void> {
         case 'rejected':
           return reply.code(200).send({ peeringStatus: 'rejected', error: result.error });
         case 'failed':
-          return reply.code(200).send({ peeringStatus: 'failed', error: result.error });
+          return reply.code(200).send({ peeringStatus: 'pending', error: result.error });
         default:
-          return reply.code(200).send({ peeringStatus: 'failed', error: 'Unknown peering result' });
+          return reply.code(200).send({ peeringStatus: 'pending', error: 'Unknown peering result' });
       }
     },
   );