Add global error handling (Phase 2) ...

- Create useGlobalErrorHandler composable that wires up three
  global error-catching surfaces:
    1. app.config.errorHandler — Vue runtime errors (render,
       watchers, lifecycle hooks, event handlers).
    2. window 'unhandledrejection' — rejected promises without catch.
    3. window 'error' — synchronous JS runtime errors.
- Create AppErrorBoundary component wrapping RouterView to catch
  Vue errors in child components and show fallback UI (AppErrorState
  with Retry) instead of a blank screen.
- Apply the boundary in App.vue so every routed page is protected.

All 126 Vitest tests pass.

Vue client: add shared area assignment to scripts and devices ...

- Add useAreaAssign composable for reusable area assignment logic
- Add AreaBadgeLink and AreaAssignSection shared components
- Integrate area assignment into ScriptDetailPage (actions/regular)
- Integrate area assignment into DeviceDetailPage
- Update scriptsStore with assignToArea / unassignFromArea + reactivity fixes
- Update API modules: scripts.placeInArea, devices.assignToArea
- Update list views: show area badges in actions/regular cards and tables
- Add tests and mock handlers for script area operations
- Update AppShell nav and routes for detail pages
- Add prism-theme.css for code highlighting
- 125 tests passing, build green