feat(client-federation): user-view cache for cross-instance DM render

Fixes a render bug where a federated user (e.g. axel@nova) appeared with
the federation globe icon and a broken avatar when viewed on his own home
instance. Root cause: `populateFromReady` is first-wins by federatedId and
discards the entire skipped DM payload — including its `members` array —
so when a sibling instance's ready arrived first, the home instance's view
of every shared user was dropped on the floor.

Adds a render-only `userViews` cache that mirrors the `dmAlternatives`
philosophy: information from skipped ready payloads is preserved for
rendering. Every wire surface that delivers a User upserts into the cache
regardless of dedup outcome; render sites read through a Zustand selector
hook to surface the home view when one is loaded. The DM channel ingestion
race is left untouched — the existing no-flapping invariant on origin
reconnect is intentional and load-bearing for failover.

Layered changes:

- `identity.ts`: `normalizeOriginToHost`, `canonicalUserKey`,
  `isDeliveryFromHome`, `isFederationGlobeApplicable` — single helpers
  for origin/host normalization and the home/stub tier decision.
- `spaceStore.ts`: `userViews` Map, `UserViewEntry` type, `upsertUserView`
  action with the home-wins preference rule, prune by `deliveredBy` in
  `removeInstanceSpaces` (mirrors `dmAlternatives` cleanup), `reset`
  clears.
- `userViewLookup.ts`: `useCanonicalUserView` (Zustand selector hook for
  React) + `getCanonicalUserView` (sync getter for non-React paths).
  Render reactivity is structural via the selector, not coincidence on
  legacy update paths.
- `populateFromReady` upsert pass runs BEFORE the federatedId dedup so
  members of skipped DMs still reach the cache.
- WS handlers (dm_message_*, message_*, user_updated, member_joined,
  friend_request_*, dm_channel_created, dm_member_added) and REST
  hydrators (socialStore, discoverStore, mutuals) feed the cache with
  their delivering origin.
- Render-site routing through `useCanonicalUserView` at every audited
  user-rendering site (sidebar, header, search, message bubble, reply
  chips, profile popout/modal, group settings, voice tiles, mention
  chips, member lists, friends, invites). Self-rendering sites compose
  alongside via existing `isSelf`/`resolveDisplayIdentity`.
- Globe predicate hoisted to `isFederationGlobeApplicable` and applied
  at three sites, gating on `domain !== window.location.host` so we
  never show the globe for users whose home IS our own.

Tests: 31 new unit tests across `identity`, `userViews` store, and
`userViewLookup`. Full suite 276/276.

Docs: `client-federation.md` §3 gains a "User View Cache" section
parallel to "DM Origin Failover"; `dm-system.md` notes the new store
action and WS handler upserts.

Bug 3 (federation profile-sync gap — orbit's stale profile data on
nova-Axel after a clear/color-change on nova never propagated)
remains open. The user-view cache routes around it for the common case
(home instance is connected), but the underlying S2S relay gap is its
own diagnosis and follows in a separate branch.

packages/web/src/hooks/useVoiceParticipantMeta.ts

@@ -1,6 +1,7 @@
 import { useMemo } from 'react';
 import { useSpaceStore } from '../stores/spaceStore';
 import { parseFederatedUsername } from '../utils/identity';
+import { getCanonicalUserView } from '../utils/userViewLookup';
 import type { ParticipantInfo } from './useLiveKit';
 import type { User } from '@backspace/shared';
 
@@ -18,11 +19,12 @@ export function useVoiceParticipantMeta(participant: ParticipantInfo) {
     // 1. Try space members (primary — covers space voice channels)
     const member = members.find(m => m.userId === participant.userId);
     if (member?.user) {
-      const { baseName } = parseFederatedUsername(member.user.username);
+      const canonical = getCanonicalUserView(member.user as User);
+      const { baseName } = parseFederatedUsername(canonical.username);
       return {
-        displayName: member.user.displayName ?? baseName,
-        avatar: member.user.avatar ?? null,
-        user: member.user as User,
+        displayName: canonical.displayName ?? baseName,
+        avatar: canonical.avatar ?? null,
+        user: canonical,
       };
     }
 
@@ -30,22 +32,26 @@ export function useVoiceParticipantMeta(participant: ParticipantInfo) {
     for (const dm of dmChannels) {
       const dmMember = dm.members?.find(m => m.id === participant.userId);
       if (dmMember) {
-        const { baseName } = parseFederatedUsername(dmMember.username);
+        const canonical = getCanonicalUserView(dmMember as User);
+        const { baseName } = parseFederatedUsername(canonical.username);
         return {
-          displayName: dmMember.displayName ?? baseName,
-          avatar: dmMember.avatar ?? null,
-          user: dmMember as User,
+          displayName: canonical.displayName ?? baseName,
+          avatar: canonical.avatar ?? null,
+          user: canonical,
         };
       }
     }
 
-    // 3. Fallback to cached user from ParticipantInfo (federation carry-forward)
+    // 3. Fallback to cached user from ParticipantInfo (federation carry-forward).
+    // Route through the userViews cache: a User captured from federation handoff
+    // can be a stale stub view, and the cache may hold a fresher home view.
     if (participant.cachedUser) {
-      const { baseName } = parseFederatedUsername(participant.cachedUser.username);
+      const canonical = getCanonicalUserView(participant.cachedUser);
+      const { baseName } = parseFederatedUsername(canonical.username);
       return {
-        displayName: participant.cachedUser.displayName ?? baseName,
-        avatar: participant.cachedUser.avatar ?? null,
-        user: participant.cachedUser,
+        displayName: canonical.displayName ?? baseName,
+        avatar: canonical.avatar ?? null,
+        user: canonical,
       };
     }