ObservabilityPage.tsx was refactored into service-tabs/; update removal
criteria to name real targets and whitelist the Dashboard.test fixture
shortcut-label collision.
5 locked design decisions: step derivation formula (max(15, round(s/200))),
shared normalize_prometheus_matrix helper in widgets/prometheus_range.py,
recharts RadialBarChart gauge w/ threshold bands, mean via client-side
avg over query_range, 3-slice plan each <=400 lines.
Source-verified: ObservabilityPage refactored into service-tabs/ (map stale).