Add annotation-aware visualizer

[harsh-sikhwal]

Summary

• Visualizer accepts either a plain infrastructure definition or the combined {infrastructure, annotations} structure returned by get_graph(INFRAGRAPH); refactored into a Visualizer class (state on self instead of threaded through function args).
• Hover tooltips in the visualizer now surface non-immutable annotation attributes on nodes and edges, in both the infrastructure-level and device/component views.
• Reorganize visualizer code

The merge-base changed after approval.