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.

docs/systems/dm-system.md

@@ -609,16 +609,18 @@ const isLocalMember = (u: { homeInstance?: string | null }) =>
 | `closeDm(id)` | Calls `api.dm.close(id)` via origin-aware API client, removes from state |
 | `leaveDm(id)` | Calls `api.dm.leave(id)` via origin-aware API client, removes from state |
 | `findExistingDmForUser(targetUser)` | Scans `dmChannels` for a 2-member DM where the other member's `homeUserId` matches the target's `homeUserId` |
+| `upsertUserView(user, deliveringOrigin)` | Inserts/updates the user-view cache under the home-wins preference rule. Called for every DM member surface (kept AND skipped channels) so render sites surface the home view even when first-wins channel dedup discarded the home payload. See `client-federation.md` §3 "User View Cache" |
 
 ### WebSocket Event Handlers (`useWebSocket.ts`)
 
 | WS Event | Handler |
 |----------|---------|
-| `dm_channel_created` | Normalize remote user assets, call `addDmChannel(channel, origin)` |
+| `dm_channel_created` | Normalize remote user assets, upsert each member into `userViews`, call `addDmChannel(channel, origin)` |
 | `dm_channel_closed` | Call `removeDmChannel(dmChannelId)` |
-| `dm_member_added` | Normalize remote user assets, call `addDmMember(dmChannelId, user)` |
+| `dm_member_added` | Normalize remote user assets, upsert into `userViews`, call `addDmMember(dmChannelId, user)` |
 | `dm_member_removed` | Call `removeDmMember(dmChannelId, userId)` |
 | `dm_owner_updated` | Call `updateDmOwner(dmChannelId, newOwnerId)` |
+| `dm_message_created` / `dm_message_updated` | Normalize message assets, upsert `message.user` and `message.replyTo?.user` into `userViews` |
 
 ### New DM Modal (`NewDmModal.tsx`)