feat(federation): queue S2S presence_update on auth/disconnect/status/activity changes

New FederationPresenceUpdatePayload + queuePresenceRelay() helper. Five WS
sites now project the native user's status (and optional activities) to all
active peers via the outbox: WS auth-success, finalizeDisconnect,
manual presence_update, activity_update, showActivity-toggle clear.

Outbox-only (no mutation-log entry) — presence is ephemeral; the upcoming
peer-activation hook re-emits a fresh snapshot so peers recovering from
unreachable converge without history replay. No-op for replicated users.

packages/shared/src/types.ts

@@ -882,7 +882,7 @@ export interface FederationRelayEvent {
     | 'friend_add' | 'friend_remove' | 'file_rejected'
     | 'dm_call_start' | 'dm_call_accept' | 'dm_call_reject' | 'dm_call_end'
     | 'dm_typing_start' | 'dm_typing_stop'
-    | 'profile_update'
+    | 'profile_update' | 'presence_update'
     | 'read_state_update'
     | 'dm_close' | 'dm_reopen';
   contextType?: 'dm' | 'friend' | 'profile';
@@ -922,6 +922,7 @@ export interface FederationRelayEvent {
     username: string;
   };
   profileUpdate?: FederationProfileUpdatePayload;
+  presenceUpdate?: FederationPresenceUpdatePayload;
   readState?: {
     user: { homeUserId: string; homeInstance: string };
     messageRef: { sourceInstance: string; sourceMessageId: string };
@@ -986,6 +987,20 @@ export interface FederationProfileUpdatePayload {
   bio: string | null;
 }
 
+/**
+ * Presence projection from a home instance to peers. Carries the user's current
+ * online status and (optionally) rich activities. Outbox-only on the wire — never
+ * written to federation_mutation_log; presence is ephemeral and stale replays on
+ * peer activation are wrong (the activation hook re-emits a fresh snapshot).
+ */
+export interface FederationPresenceUpdatePayload {
+  homeUserId: string;
+  homeInstance: string;
+  status: 'online' | 'idle' | 'dnd' | 'offline';
+  activities?: Activity[];
+  ts: number; // emitter clock; receiver may use for last-write-wins
+}
+
 export interface FederationFriendshipPayload {
   from: FederationRelayParticipant;
   to: FederationRelayParticipant;