fix: use space gradients for mutual space avatars and add federation indicators in profile modal

Space avatars in the mutual spaces tab now use getSpaceGradient() instead of
a flat grey background, matching the sidebar appearance. Mutual friends and
spaces from remote instances show a globe icon with the instance hostname.
Also wires up federated mutuals loading, correct API client routing for
remote user profiles, and the new mutuals utility.

packages/web/src/components/modals/NewDmModal.tsx

@@ -3,7 +3,7 @@ import { useNavigate } from 'react-router-dom';
 import { Modal } from '../ui/Modal';
 import { Avatar } from '../ui/Avatar';
 import { useUIStore } from '../../stores/uiStore';
-import { useSpaceStore } from '../../stores/spaceStore';
+import { useSpaceStore, getApiForOrigin, resolveUserOrigin } from '../../stores/spaceStore';
 import { api } from '../../api/client';
 import type { User } from '@backspace/shared';
 
@@ -66,8 +66,10 @@ export function NewDmModal() {
         navigate(`/channels/@me/${existing.dm.id}`);
         return;
       }
-      const channel = await api.dm.create({ userId: user.id });
-      addDmChannel(channel);
+      const origin = resolveUserOrigin(user);
+      const dmApi = getApiForOrigin(origin);
+      const channel = await dmApi.dm.create({ userId: user.id });
+      addDmChannel(channel, origin);
       closeModal();
       useUIStore.getState().setShowDms(true);
       navigate(`/channels/@me/${channel.id}`);