25076dc1f3
Implements story 2-6: Renderer class with per-aircraft trail history (deque capped at TRAIL_MAX_DOTS=5), NullDisplay with DEBUG logging, WaveshareDisplay stub, and end-to-end pipeline smoke test. All 96 tests pass; ruff check and format clean. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>