fix(visualization): address CodeRabbit review findings

- Reset suppressedLabel on clearLabels/clearTemporaryLabel to prevent
  stale references after map re-renders
- Skip suppressed (invisible) labels in collision detection so they
  don't push visible labels unnecessarily
- Add afterEach in codeMapBuilding.spec.ts to restore ColorConverter
  after tests and prevent within-file mock leakage

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