feat: LWW timestamps for bidirectional federation profile & layout sync

Profile and space layout changes on remote instances were being
overwritten by stale data on reconnect. Adds Last-Writer-Wins
timestamps so the client-relay mesh rejects stale writes:

- profile_updated_at column on users table with migration + backfill
- Server LWW guards on PATCH /users/@me and PUT /space-layout
- Bidirectional profileSync: pulls newer remote profiles to home
- LWW layout sync replaces home-authoritative _layoutFromTrueHome flag
- Layout pushes to ALL connected instances in parallel

packages/server/src/utils/sanitize.ts

@@ -17,6 +17,7 @@ export function sanitizeUser(row: typeof schema.users.$inferSelect): User {
       customStatus: null,
       isAdmin: false,
       isDeleted: true,
+      profileUpdatedAt: 0,
       createdAt: row.createdAt,
       homeInstance: null,
       homeUserId: null,
@@ -45,6 +46,7 @@ export function sanitizeUser(row: typeof schema.users.$inferSelect): User {
     status: (row.status ?? 'offline') as User['status'],
     customStatus: row.customStatus,
     isAdmin: row.isAdmin === 1,
+    profileUpdatedAt: row.profileUpdatedAt ?? row.createdAt,
     createdAt: row.createdAt,
     homeInstance: row.homeInstance ?? null,
     homeUserId: row.homeUserId ?? null,