review(2-4): pass story 2-4 — altitude colour bands & aircraft type icons

All 7 ACs verified. No code fixes required: boundary logic (<=), category
map, callsign prefix guard, altitude fallback thresholds, empty-category
guard, and type annotations are all correct. 89/89 tests pass, ruff clean.

Added two deferred items: hardcoded _AIRLINE_PREFIXES subset and A-category
military aircraft misclassification. Story and sprint-status marked done.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

_bmad-output/implementation-artifacts/sprint-status.yaml

@@ -35,7 +35,7 @@
 # - Dev moves story to 'review', then runs code-review (fresh context, different LLM recommended)
 
 generated: 2026-04-22
-last_updated: 2026-04-22  # 2-1 done, 2-2 done, 2-3 done, 2-4 review, epic-2 in-progress
+last_updated: 2026-04-22  # 2-1 done, 2-2 done, 2-3 done, 2-4 done, epic-2 in-progress
 project: planeMapper
 project_key: NOKEY
 tracking_system: file-system
@@ -56,7 +56,7 @@ development_status:
   2-1-aircraft-data-model-and-fetcher: done
   2-2-coordinate-projection-and-base-map-loading: done
   2-3-home-marker-and-airspace-outlines: done
-  2-4-altitude-colour-bands-and-aircraft-type-icons: review
+  2-4-altitude-colour-bands-and-aircraft-type-icons: done
   2-5-per-aircraft-drawing: backlog
   2-6-stateful-renderer-and-display-interface: backlog
   2-7-operational-radar-loop-startup-screen-and-systemd-wiring: backlog