fix(federation): resolve code review issues in upload size mismatch

- Fix critical: outbox worker now copies file_rejected payload fields
  (attachmentId, sourceFilename, rejectionReason, rejectionLimit,
  affectedUserIds) so the reverse relay actually delivers them
- Fix: add sourceFilename to file_rejected event for reliable
  multi-attachment matching on the sender side
- Fix: change text-accent-warning to text-accent-amber (valid class)
- Add Array.isArray guard on federationMeta parse

packages/shared/src/types.ts

@@ -770,6 +770,7 @@ export interface FederationRelayEvent {
   friendship?: FederationFriendshipPayload;
   // file_rejected event fields
   attachmentId?: string;
+  sourceFilename?: string;
   rejectionReason?: string;
   rejectionLimit?: number;
   affectedUserIds?: string[];