types(web): unify FederationPeer with shared type

packages/web/src/api/client.ts declared a local FederationPeer that had
drifted from @backspace/shared: it loosened `status` to `string` (losing
the exhaustive 7-value union) and widened `consecutiveFailures` and
`lastSyncedAt` to `number | null`. The latter two are spurious — the
server never returns null for either — and `status: string` defeated
the compiler's ability to flag a missed case when `rejected`,
`awaiting_approval`, or `needs_attention` were added over the course
of the auto-peering / approval-queue / outbox-auth-failure-recovery
work.

Replace the local interface with a re-export of the shared type. All
three status switches in FederationPanel.tsx (peerStatusColor,
peerStatusDotColor, peerStatusLabel) and the StatusFilter union were
already exhaustive over the 7 values, so no behaviour change is
needed — the re-export just pins the compile-time contract.

web tsc --noEmit is clean after the swap.

Follow-up #23 from S2S DM unification backlog.

packages/web/src/api/client.ts

@@ -52,8 +52,11 @@ import type {
   FederationRegistryEntry,
   FederationIdentityDeleteRequest,
   FederationIdentityDeleteResponse,
+  FederationPeer,
 } from '@backspace/shared';
 
+export type { FederationPeer };
+
 export class RateLimitError extends Error {
   readonly retryAfter: number;
   constructor(retryAfter: number) {
@@ -63,22 +66,6 @@ export class RateLimitError extends Error {
   }
 }
 
-export interface FederationPeer {
-  id: string;
-  origin: string;
-  instanceName: string | null;
-  status: string;
-  lastSeenAt: number | null;
-  lastFailureAt: number | null;
-  consecutiveFailures: number | null;
-  consecutiveAuthFailures: number;
-  lastSyncedAt: number | null;
-  createdAt: number;
-  secretRotatedAt: number | null;
-  rotationInProgress: boolean;
-  autoRotateIntervalDays: number;
-}
-
 export interface ApprovalRequest {
   id: string;
   origin: string;