fix(server): canonicalize spaceInstanceOrigin before storing payload

Empty-string (local) origin is now stored as the absolute home origin
so relayed DM space-invite cards carry the correct value to remote
recipients instead of resolving against the wrong instance.

packages/server/src/routes/dm.ts

@@ -1757,7 +1757,7 @@ export async function dmRoutes(app: FastifyInstance): Promise<void> {
     const payload: SpaceInviteSystemPayload = {
       event: 'space_invite',
       spaceId: body.spaceId,
-      spaceInstanceOrigin: body.spaceInstanceOrigin,
+      spaceInstanceOrigin: spaceOrigin,
       inviteCode: body.inviteCode,
       snapshot: {
         spaceName: snapshot.spaceName,