feat: capability heatmap visualization

[rajnavakoti]

Description

Add a heatmap visualization that shows business capabilities colored by health/maturity metrics. Each capability is a cell in the heatmap, colored by a configurable dimension (maturity, sourcing, investment, risk). This gives leadership a one-glance view of where the architecture is strong vs. needs attention.

Acceptance Criteria

• Heatmap grid layout with one cell per business capability
• Configurable color dimension: maturity, status, sourcing, or custom field
• Cells are clickable — navigate to the capability detail page
• Shows capability name and the metric value in each cell
• Domain grouping (capabilities grouped by their parent domain)
• Driven by a heatmap-mapping.yaml config file (follows the 2-tier map pattern)
• Responsive layout that works on different screen sizes

Out of Scope

• Editable metrics from the heatmap (read-only view)
• Time-series heatmaps (single point-in-time snapshot)