Implements a typed mesh snapshot API in `@fusion/core` (`CentralCore.getMeshSnapshot`, `MeshSnapshot` type) and wires it through the dashboard nodes view via a new `useMeshState` hook, substantially simplifying `MeshTopology.tsx` by replacing internal state management with the centralized snapshot.
Fusion-Task-Id: FN-3454
- Update node management UI components to use shared form/button classes, semantic color tokens, and accessible interactions
- Refine mesh topology rendering and related dashboard tests for improved readability and behavior coverage
- Adjust discovery routes to reuse injected centralCore instances without unnecessary init/close cycles
- Add/extend tests for shared CentralCore discovery flows and model settings scope save behavior
- Export MeshTopologyProps interface for external use
- Add peer awareness lines between remote nodes for mesh visualization
- Implement dynamic SVG sizing based on number of remote nodes
- Add status color legend showing online/offline/connecting/error states
- Improve CSS variable handling with fallback values
- Use transform-based positioning for cleaner SVG structure
