Seven pure-math helpers in the new RetailChaseCamera class:
ComputeHeading (slope-align with flat fallback), BuildBasis (heading
→ orthonormal frame, near-vertical fallback), PushVelocity +
AverageVelocity (5-entry FIFO ring), ComputeDampingAlpha (retail's
stiffness*dt*10), FilterMouseAxis (0.25s low-pass), ComputeTranslucency
(linear ramp 0.20..0.45 m). 20 tests, all pass. State machine + Update()
land in the next commit.
Per spec docs/superpowers/specs/2026-05-18-retail-chase-camera-design.md.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
