Shared theme/plots:
- Softer professional palette, refined rc params, higher tint alphas
- ref_lines: place value labels inside the axes (never clipped)
- legend_outside helper; br_heatmap legends only categories present in grid

Per-area fixes from the adversarial visual re-verify:
- correlated: collapse coincident CE/CCE into one "CE = CCE region";
  welfare bars get value labels + a 0 baseline
- stochastic: Q-heatmap uses constrained_layout with a right-side colorbar;
  cheap-talk equilibrium regions legend moved outside the plot
- bayesian: second-price sweep reframed as "truthful bid is weakly dominant";
  VCG example made competitive so a real externality payment shows, with
  per-bar value labels so a $0 payment reads explicitly

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>