Release: 0.2.1

feat: adjustable radius API (#18)

* fix: add radius parameter to FrameMonitor and threshold to FrameCoverage

  Previously FrameMonitor used hardcoded RADIUS from env var, inconsistent
  with BKFrameMonitor and RustBKFrameMonitor which accept radius in their
  constructors. This change makes all monitors consistent.

  - Add FrameMonitor(radius=) constructor parameter
  - Add FrameCoverage(threshold=) constructor parameter
  - Add threshold parameter to get_frame_cov()
  - Create docs/api.md with comprehensive API reference
  - Update docs/frame_cov.md configuration section

* ignore fuzz link

* radius API analysis

* feat: change default RADIUS from 5 to 10

  Based on empirical analysis of Zelda fuzzing dataset:
  - radius=5: linear growth, no convergence (growth rate 0.55)
  - radius=10: converging behavior (growth rate 0.36)

  The new default provides better convergence characteristics
  for games with high visual entropy while still distinguishing
  meaningfully different game states.

  See radius_analysis_report.md for full experimental results.

* bump version

Release 0.2.0

Rust core.