feat(phase-6): rich super admin dashboard UI

Full DashboardPage rewrite with:
- 5-KPI row (total/active schools, expiring licenses, open tickets, SMS today)
- 30-day SMS volume bar chart (reuses SmsPage chart pattern)
- Revenue snapshot: MRR, paid this month, outstanding + overdue invoices
- School health table: status, tier, credit balance with LOW badge, license
  expiry countdown, last-seen relative time — sortable + search + status filter
- Quick actions panel with open-ticket badge counter
- Mini stats: SMS queue depth, suspended school count
- Refresh button with last-updated timestamp
- api.ts: getDashboardSchoolHealth + getDashboardRevenue

.paul/ROADMAP.md

@@ -19,8 +19,8 @@ SMS flow: On-prem TapTrack polls Hub every 30s → Hub queues SMS jobs → Hub s
 ## Current Milestone
 
 **v1.0 — Foundation & Core Services**
-Status: Phase 5 complete — Phase 6 next
-Phases: 5 of 15 complete
+Status: Phase 6 complete — Phase 7 next
+Phases: 6 of 15 complete
 
 ---
 
@@ -33,7 +33,7 @@ Phases: 5 of 15 complete
 | 3     | On-Prem License Validation     | 1   | ✅ Complete  | 2026-03-15 |
 | 4     | SMS Gateway (credits + queue)  | 2   | ✅ Complete  | 2026-03-15 |
 | 5     | On-Prem SMS Polling Agent      | 1   | ✅ Complete  | 2026-03-16 |
-| 6     | Super Admin Dashboard UI       | TBD | Not started  | —          |
+| 6     | Super Admin Dashboard UI       | 1   | ✅ Complete  | 2026-03-16 |
 | 7     | School Admin Portal UI         | TBD | Not started  | —          |
 | 8     | Billing Engine + Invoice PDF   | TBD | Not started  | —          |
 | 9     | Email Dispatcher               | TBD | Not started  | —          |