feat: add CLI Viewer Page with multi-pane layout and state management

- Implemented the CliViewerPage component for displaying CLI outputs in a configurable multi-pane layout.
- Integrated Zustand for state management, allowing for dynamic layout changes and tab management.
- Added layout options: single, split horizontal, split vertical, and 2x2 grid.
- Created viewerStore for managing layout, panes, and tabs, including actions for adding/removing panes and tabs.
- Added CoordinatorPage barrel export for easier imports.

ccw/frontend/src/locales/en/execution-monitor.json

@@ -3,6 +3,9 @@
     "title": "Execution Monitor",
     "subtitle": "View real-time execution status and history"
   },
+  "actions": {
+    "openCliViewer": "CLI Monitor"
+  },
   "currentExecution": {
     "title": "Current Execution",
     "noExecution": "No workflow is currently executing",