feat(phase-4): SMS gateway dashboard + stats + health + retry

Backend (backend/app/routers/sms.py):
- GET /api/sms/stats: aggregate totals by status, daily volume chart
  (configurable N days), per-school top-10 breakdown, delivery rate,
  live queue depth
- POST /api/sms/jobs/{id}/retry: reset failed/cancelled job to pending
- GET /api/sms/health: Semaphore API connectivity check + credit balance
- POST /api/sms/trigger-queue: manually fire sms.process_queue Celery task

Frontend (frontend/src/pages/SmsPage.vue) — rebuilt from scratch:
- Semaphore health badge with live status indicator and balance display
- 'Process Queue' button calling POST /api/sms/trigger-queue
- KPI row: Total, Sent, Failed, Pending (queue depth), Delivery Rate %;
  period picker switching between 7/30/90 day views
- Volume bar chart: daily sent vs failed bars with hover tooltips,
  x-axis date labels, legend; no charting library required
- School breakdown panel: top 10 schools by volume with delivery
  percentage bars
- Jobs table: status + school + phone number filters; inline error
  message on failed rows; Retry button for failed/cancelled jobs;
  retry count display; pagination

api.ts: getSmsStats, retrySmsJob, getSmsHealth, triggerSmsQueue

PAUL: Phase 4 marked complete, STATE + ROADMAP updated

.paul/STATE.md

@@ -3,10 +3,10 @@
 ## Current Position
 
 Milestone: v1.0 — Foundation & Core Services
-Phase: 3 of 15 (On-Prem License Validation — complete)
-Plan: Phase 3 complete — Phase 4 next
-Status: **Phase 3 applied — ready to begin Phase 4**
-Last activity: 2026-03-15 — Phase 3 complete (TapTrack on-prem: license validation task, startup check, hub router, frontend warning banner)
+Phase: 4 of 15 (SMS Gateway — complete)
+Plan: Phase 4 complete — Phase 5 next
+Status: **Phase 4 applied — ready to begin Phase 5**
+Last activity: 2026-03-15 — Phase 4 complete (SMS stats/health/retry/trigger endpoints + full SmsPage dashboard with chart, KPIs, school breakdown)
 
 ## Loop Position
 
@@ -22,7 +22,7 @@ PLAN ──▶ APPLY ──▶ UNIFY
 - Phase 1  (Project Setup & Infrastructure): [██████████] 100% ✓
 - Phase 2  (School Registry + License Mgmt): [██████████] 100% ✓
 - Phase 3  (On-Prem License Validation):     [██████████] 100% ✓
-- Phase 4  (SMS Gateway):                    [░░░░░░░░░░]   0%
+- Phase 4  (SMS Gateway):                    [██████████] 100% ✓
 - Phase 5  (On-Prem SMS Polling Agent):      [░░░░░░░░░░]   0%
 - Phase 6  (Super Admin Dashboard UI):       [░░░░░░░░░░]   0%
 - Phase 7  (School Admin Portal UI):         [░░░░░░░░░░]   0%
@@ -37,8 +37,8 @@ PLAN ──▶ APPLY ──▶ UNIFY
 
 ## Next Action
 
-Run: `/paul:plan` for Phase 4 — SMS Gateway (credits + queue)
-Resume file: .paul/ROADMAP.md → Phase 4
+Run: `/paul:plan` for Phase 5 — On-Prem SMS Polling Agent
+Resume file: .paul/ROADMAP.md → Phase 5
 
 ## Repo