Replace sample dashboard cards with extensible operational widgets

[sfmskywalker]

Summary

• retain and deepen the Dashboard Widget SDK with any-number-per-module contributions, host-owned frames, sizing, refresh, timeout/stale controls, layout preferences, and runtime isolation
• replace the valueless sample cards with Attention, Workflow Portfolio, and Workflow Run Health widgets
• add correlated/snoozable Attention, exact workflow aggregates, date-range/test-run settings, responsive/accessibility behavior, and scoped preference persistence
• remove the obsolete sample Dashboard module without a migration path
• document the architecture and contracts; capture all deferred extensions as Add Structured Logs Attention integration #316–Evaluate a dedicated Attention route #332 and outdated-doc correction as Update outdated Studio architecture-tour documentation #333

Verification

• typecheck, lint (0 errors), all Vitest suites, and all production builds passed
• Elsa.Studio.Tests 381/381 passed
• real-browser proof covered exact seeded 105-definition/125-run aggregates, independent refresh, partial Attention failure, correlation, snooze persistence, reorder/resize/hide/restore persistence, responsive layout, accessibility, and clean console/network behavior

Backend/API companion: elsa-workflows/elsa-foundation#653.

Closes #312
Closes #313
Closes #314
Closes #315