feat(031): Maintenance Banner for Dashboards — full spec→plan→tasks package
Spec: 5 user stories (P1-P3), 17 FRs, 7 SCs, 12 edge cases, RBAC matrix
Plan: 7 research decisions, 15 semantic contracts (C1-C4)
Data: 4 SQLAlchemy models (Banner entity enforces one-chart-per-dashboard)
UX: async-only API, banner template with optional variables, admin settings UI
Tasks: 64 tasks across 8 phases, 12 reused frontend components
Workflow: component reuse scan mandated in speckit.plan/tasks + semantics-svelte
Constitution: filled with 7 architecture principles from ADRs