feat(multiuser): phase 4, event fan-out + stream scoping

Scopes real-time streams and the init snapshot so a multi-user client only
receives what it owns. No-op in single-user mode (identity-less clients).

- WS terminal (ws-routes): owner gate after the session lookup. A non-admin may
  only attach to their own session (close 4003); the global auth hook already
  ran on the upgrade and decorated req.authUser, so an unauthenticated upgrade
  never reaches the handler.
- SSE (sse-stream-manager): per-client identity stored at addClient; broadcast()
  and the terminal-batch flush both enforce a routing hint via canDeliver().
  WebServer.broadcast auto-derives the hint (deriveSseHint): session-scoped event
  families resolve the owner from the payload's session id (fail closed when the
  owner can't be resolved), machine-level families (docker/tunnel/update/system/
  cron) + host-plan telemetry are admin-only, everything else stays global. Raw
  terminal bytes resolve the owner once and are withheld from non-owners.
- getLightState is filtered per connection AFTER the shared cache (sessions,
  respawnStatus, subagents, workflowRuns by owner; scheduledRuns + planUsage
  admin-only); applied to both the SSE init snapshot and GET /api/status.
- file-routes: getKnownSessionWorkingDir + getSessionAttachmentHistory (the
  preview/thumbnail/history helpers that bypass findSessionOrFail) now owner-check
  the session, closing a cross-user file-read path.
- GET /api/search: harvestSources is owner-scoped.

Deferred to a follow-up (documented in docs/multi-user-plan.md): away-digest +
subagent/workflow REST list scoping, push-subscription identity + routing,
per-user screenshot subdirs. The live-event versions of these are already routed
by the SSE hint; only the on-demand REST aggregates remain global for admins-only
follow-up.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/web/routes/system-routes.ts

@@ -139,7 +139,7 @@ export function registerSystemRoutes(
 
   // ========== Status ==========
 
-  app.get('/api/status', async () => ctx.getLightState());
+  app.get('/api/status', async (req) => ctx.getLightState(req.authUser));
 
   // ========== Tunnel ==========