feat(phase-9): email dispatcher — HTML templates, delivery log, test endpoint

Backend:
- app/models/email_log.py: EmailLog table (school_id, to, subject, type, status,
  error, sent_at) with EmailType + EmailStatus enums
- migrations/002_phase9_email_logs.py: Alembic migration for email_logs table
- app/templates/email/: 6 Jinja2 HTML templates — base layout, invoice,
  low_credit, license_expiry, overdue_warning, suspension
- app/services/email.py: enhanced send_email() — accepts template_name+context
  for HTML rendering, logs every attempt to email_logs, retries up to 3x on
  transient SMTP failure with exponential backoff
- app/routers/email.py: GET /api/email/logs (paginated, filterable by type/status/school),
  POST /api/email/test (send test email, super admin)
- tasks/billing.py: invoice + overdue warning + suspension emails now use HTML templates
- tasks/sms.py: low credit alert now uses HTML template
- tasks/license.py: expiry warning now uses HTML template
- app/main.py + migrations/env.py: wire in email_log model + email router

Frontend:
- EmailLogsPage.vue: table with to/subject/type badge/status badge/sent_at/error,
  type+status filters, pagination, Send Test Email modal
- router/index.ts: /email-logs route
- AppSidebar.vue: Email Logs nav item
- api.ts: getEmailLogs, sendTestEmail

.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 8 complete — Phase 9 next
-Phases: 8 of 15 complete
+Status: Phase 9 complete — Phase 10 next
+Phases: 9 of 15 complete
 
 ---
 
@@ -36,7 +36,7 @@ Phases: 8 of 15 complete
 | 6     | Super Admin Dashboard UI       | 1   | ✅ Complete  | 2026-03-16 |
 | 7     | School Admin Portal UI         | 1   | ✅ Complete  | 2026-03-16 |
 | 8     | Billing Engine + Invoice PDF   | 1   | ✅ Complete  | 2026-03-16 |
-| 9     | Email Dispatcher               | TBD | Not started  | —          |
+| 9     | Email Dispatcher               | 1   | ✅ Complete  | 2026-03-16 |
 | 10    | Support Ticket System          | TBD | Not started  | —          |
 | 11    | Monthly Report Generation      | TBD | Not started  | —          |
 | 12    | On-Prem Monthly Report Pull    | TBD | Not started  | —          |