[codex] Fix workspace synchronization

[oscharko]

Summary

Fixes #1540 by synchronizing the desktop workspace state across open Keiko clients.

Root Cause

The workspace hook hydrated and persisted windows/connections through browser-local localStorage, but it did not subscribe to changes written by another tab. Because localStorage is browser-local, a second browser also had no shared source of truth and could show the empty workspace while another browser had active windows.

Changes

• Added a bounded local BFF workspace-state snapshot endpoint at GET/PUT /api/workspace/state.
• Updated useWorkspace to:
  • adopt storage events from other tabs in the same browser profile,
  • publish sanitized workspace snapshots to the local BFF,
  • poll and adopt newer BFF snapshots from other browsers,
  • avoid echoing remote snapshots back as new local writes.
• Added regression coverage for cross-tab adoption and the server snapshot endpoint.

Validation

• npm run build:packages
• npm test --workspace @oscharko-dev/keiko-ui -- useWorkspace.keyboard.test.tsx workspace-persistence.test.ts
• npm run typecheck --workspace @oscharko-dev/keiko-ui
• npx vitest run packages/keiko-server/src/routes.test.ts packages/keiko-server/src/server.test.ts
• npx prettier --check packages/keiko-ui/src/app/components/desktop/hooks/useWorkspace.ts packages/keiko-ui/src/app/components/desktop/hooks/useWorkspace.keyboard.test.tsx packages/keiko-server/src/routes.ts packages/keiko-server/src/server.test.ts packages/keiko-server/src/workspace-state-handlers.ts