v0.15.0

feat(v0.15.0): dashboard / orchestrator-view as default landing

App now opens to a dashboard listing every session as a large card,
inspired by Anthropic's Agent View. Cards show title, status pill
(live / 승인 대기 / idle), relative last-activity time, currently
running worker chips (worker-colored pulse dot), and a 3-line preview
of the most recent message. Hover reveals 이름/삭제. Click anywhere on
a card to enter that session's full 3-panel view.

  - src/Dashboard.tsx (new): grid component with SessionCard, empty
    state, and '+ 새 세션' button
  - src/App.tsx: persisted view state ('dashboard' | 'session') in
    localStorage; conditional render of Dashboard vs the existing
    3-panel layout; helpers enterSession / newSession that set
    activeSessionId and flip view
  - TopBar logo becomes '← Multi-Agent Console' when in session view,
    clicking returns to the dashboard

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>