Graph: Support logical grouping by Area for mesh visualization

[DarinShapiro]

Description

Improve the mesh visualization by supporting logical grouping of nodes by their Home Assistant Area.

User Intent / Expected UX

The Cytoscape graph should visually group or cluster nodes by Area to provide better spatial/logical context of the Thread mesh.

Current UX Limitation

Nodes are displayed without clear logical grouping by physical area, making large meshes harder to interpret.

Evidence

Reported during live review of v0.11.32.

[DarinShapiro]

Closing as part of shipped dashboard work in versions 0.11.33/0.11.34.