fix(voice): push voice presence to user on mid-session space join

Voice presence (voiceStates/voiceUserStates/spaceVoiceStates) was only ever
delivered in the WS `ready` payload — i.e. at connect/reload. A user joining a
space mid-session got `member_joined` (no voice data) and a bare space object;
`GET /api/spaces/:id` (the channel-sidebar hydrator) carries no voice state
either. So members already sitting in a voice channel stayed invisible in the
new member's sidebar until a full page reload.

Fix at the systemic root: ConnectionManager.addUserSpace — the single chokepoint
every join path funnels through (invite, public join, join-request approval),
and which is NOT used on reconnect (that path uses setUserSpaces) — now pushes a
scoped `space_voice_state` snapshot to the joining user. The snapshot is built by
a new buildSpaceVoiceState(spaceId, userId) helper that is also the single source
of truth feeding buildReadyPayload (refactored to use it), so the connect-time
and join-time paths can never drift.

Robustness:
- Delivered over the same ordered WebSocket as voice_state_update deltas — no
  REST snapshot-vs-event-stream race.
- VIEW_CHANNEL-filtered via computePermissions exactly like `ready`: a joiner is
  never told who occupies a voice channel they cannot see.
- Client applies it scoped to the space (utils/voiceStateSync.applySpaceVoiceState):
  merges occupants/statuses and rebuilds only that space's restriction keys,
  never disturbing voice state in other spaces.
- Skipped when the space has no active voice and no restrictions (e.g. space
  creation).

Tests: server helper behavior, the join push, and private-channel exclusion;
client scoped-apply. Specs updated (websocket.md, voice.md, spaces.md).

packages/shared/src/types.ts

@@ -442,6 +442,7 @@ export type ServerEvent =
   | { type: 'dm_call_ended'; dmChannelId: string }
   | { type: 'dm_call_undeliverable'; dmChannelId: string | null; federatedCallId: string; terminal: boolean; phase: DmCallPhase; failures: DmCallUndeliverableFailure[] }
   | { type: 'voice_status_update'; userId: string; channelId: string; isMuted: boolean; isDeafened: boolean; isCameraOn: boolean; isScreenSharing: boolean }
+  | { type: 'space_voice_state'; spaceId: string; voiceStates: Record<string, string[]>; voiceUserStates: Record<string, { isMuted: boolean; isDeafened: boolean; isCameraOn: boolean; isScreenSharing: boolean }>; spaceVoiceStates: Record<string, { spaceMuted: boolean; spaceDeafened: boolean; permissionMuted: boolean }> }
   | { type: 'dm_channel_created'; dmChannel: DmChannel }
   | { type: 'dm_channel_closed'; dmChannelId: string }
   | { type: 'dm_channel_updated'; dmChannelId: string; name: string | null; icon: string | null }