Add missing -> PhaseResult return type annotation to _make_phase helper in TestPhaseTimelineDotColoring

[decko]

Finding\n\nFile: tests/test_report_html.py:3308\nSeverity: Minor\n\nThe _make_phase helper method in TestPhaseTimelineDotColoring lacks a -> PhaseResult return type annotation. This is slightly below ideal type-safety standards, though it is consistent with the existing pattern in the TestSortPhases helper.\n\n## Suggestion\n\nAdd a -> PhaseResult return annotation to the method signature. This may require moving the import to the method signature level or using a string annotation. Low priority since it matches the existing pattern.\n\n## References\n\n- Identified during review of ticket RAKI-271 (fix: TestPhaseTimelineDotColoring assertions are vacuous due to CSS class definitions in template)