plan: add issue #403 to BACKLOG.md TODO after code quality review

Author: krystophny

BACKLOG.md

@@ -12,6 +12,7 @@
 
 **Infrastructure & Documentation Issues (Lower Priority)**
 - [ ] #388: Fix - investigate test_mpeg_consolidated failure unrelated to ylabel rotation (test infrastructure)
+- [ ] #403: Refactor - reduce contour function complexity - functions exceed 50-line target
 
 ## DOING (Current Work)
 - [x] #401: Fix - CI test-coverage failing with segfaults in colored_contours and ascii_heatmap_demo (branch: fix-ci-segfaults-401)