Brain visualization: render strategy evolution and prior landscape

[johanity]

Problem

The brain accumulates rich data (priors across topics, strategy fitness, evolution history, calibration over time) but there's no way to visualize it.

Proposed solution

Add a why --viz command that generates a simple terminal or HTML visualization:

1. Strategy evolution timeline — which strategies were killed, which spawned, current fitness
2. Prior landscape — heatmap of topic categories by usefulness prior
3. Calibration curve — prediction accuracy over time
4. Surprise distribution — histogram of surprise values

Keep it lightweight — no heavy dependencies. Consider rich for terminal rendering or a single-file HTML export.

Why this matters

Visualization makes the learning tangible. Users can see the brain getting smarter. This is the core differentiator — no other research tool shows you how it's improving.