feat(federation): hook outbox and mutation log into DM message and reaction handlers

Wire appendMutationLog + queueOutboxEvent + buildRelayPayload into all
DM mutation paths so federation peers receive relay events:

- REST: POST /api/dm/:id/messages, PATCH /api/dm/messages/:id,
  DELETE /api/dm/messages/:id
- WebSocket: dm_message_create, dm_message_edit, dm_message_delete,
  reaction_add (DM path), reaction_remove (DM path)
- Fix buildRelayPayload parameter types to accept optional replyToId
  and editedAt (matching DmMessageWithUser's optional fields)

packages/server/src/routes/dm.ts

@@ -21,6 +21,7 @@ import {
 import { sanitizeUser } from '../utils/sanitize.js';
 import { deleteUploadFile, deleteAttachmentFiles } from '../utils/fileCleanup.js';
 import { fetchDmEmbedsForMessages, resolveEmbeds, reResolveEmbeds, embedRowToEmbed } from '../utils/embedResolver.js';
+import { appendMutationLog, queueOutboxEvent, buildRelayPayload } from '../utils/federationOutbox.js';
 
 /**
  * Batch-fetch reactions for a set of DM message IDs.
@@ -970,6 +971,12 @@ export async function dmRoutes(app: FastifyInstance): Promise<void> {
     // Broadcast to all DM members (including those who closed the channel)
     broadcastDmMessage(id, message);
 
+    // Federation: log mutation and queue for relay
+    appendMutationLog(messageId, id, 'create');
+    queueOutboxEvent(messageId, id, 'create', JSON.stringify({
+      message: { ...buildRelayPayload(message, message.user), attachments: [] },
+    }));
+
     // Resolve embeds asynchronously after responding
     setImmediate(() => {
       resolveEmbeds(messageId, content?.trim() || null, id, true, null).catch(() => {});
@@ -1031,6 +1038,12 @@ export async function dmRoutes(app: FastifyInstance): Promise<void> {
       });
     }
 
+    // Federation: log mutation and queue for relay
+    appendMutationLog(id, msg.dmChannelId, 'update');
+    queueOutboxEvent(id, msg.dmChannelId, 'update', JSON.stringify({
+      message: buildRelayPayload(updated, updated.user),
+    }));
+
     // Resolve new embeds asynchronously (old ones already deleted above)
     setImmediate(() => {
       resolveEmbeds(id, content.trim(), msg.dmChannelId, true, null).catch(() => {});
@@ -1093,6 +1106,10 @@ export async function dmRoutes(app: FastifyInstance): Promise<void> {
       });
     }
 
+    // Federation: log mutation and queue for relay
+    appendMutationLog(id, msg.dmChannelId, 'delete');
+    queueOutboxEvent(id, msg.dmChannelId, 'delete', JSON.stringify({ deleted: true }));
+
     return reply.code(200).send({ success: true });
   });
 }