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

backend/app/routers/email.py

@@ -0,0 +1,94 @@
+"""Email log viewer and test-email endpoint."""
+from typing import Optional
+from fastapi import APIRouter, Depends, Query
+from pydantic import BaseModel, EmailStr
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy import select, func, desc
+
+from app.auth.dependencies import require_super_admin
+from app.database import get_db
+from app.models.user import HubUser
+from app.models.email_log import EmailLog, EmailType, EmailStatus
+
+router = APIRouter(prefix="/api/email", tags=["email"])
+
+
+@router.get("/logs")
+async def list_email_logs(
+    email_type: Optional[EmailType] = Query(None),
+    status: Optional[EmailStatus] = Query(None),
+    school_id: Optional[str] = Query(None),
+    page: int = Query(1, ge=1),
+    per_page: int = Query(50, ge=1, le=200),
+    _admin: HubUser = Depends(require_super_admin),
+    db: AsyncSession = Depends(get_db),
+):
+    """Paginated email delivery history — super admin only."""
+    stmt = select(EmailLog).order_by(desc(EmailLog.created_at))
+
+    if email_type:
+        stmt = stmt.where(EmailLog.email_type == email_type)
+    if status:
+        stmt = stmt.where(EmailLog.status == status)
+    if school_id:
+        stmt = stmt.where(EmailLog.school_id == school_id)
+
+    total = (await db.execute(select(func.count()).select_from(stmt.subquery()))).scalar_one()
+    logs = (await db.execute(stmt.offset((page - 1) * per_page).limit(per_page))).scalars().all()
+
+    return {
+        "items": [
+            {
+                "id": log.id,
+                "school_id": log.school_id,
+                "to_email": log.to_email,
+                "subject": log.subject,
+                "email_type": log.email_type.value,
+                "status": log.status.value,
+                "error_message": log.error_message,
+                "sent_at": log.sent_at.isoformat() if log.sent_at else None,
+                "created_at": log.created_at.isoformat(),
+            }
+            for log in logs
+        ],
+        "total": total,
+        "page": page,
+        "per_page": per_page,
+    }
+
+
+class TestEmailBody(BaseModel):
+    to: EmailStr
+
+
+@router.post("/test")
+async def send_test_email(
+    body: TestEmailBody,
+    _admin: HubUser = Depends(require_super_admin),
+):
+    """Send a test email to verify SMTP configuration."""
+    from app.services.email import send_email
+
+    success = send_email(
+        to=body.to,
+        subject="TapTrack Hub — SMTP Test Email",
+        body=(
+            "This is a test email from TapTrack Hub.\n\n"
+            "If you received this, your SMTP configuration is working correctly.\n\n"
+            "TapTrack Hub Team"
+        ),
+        html=(
+            "<div style='font-family:sans-serif;max-width:480px;margin:32px auto;padding:24px;"
+            "background:#fff;border:1px solid #e2e8f0;border-radius:12px'>"
+            "<h2 style='color:#1e40af;margin:0 0 16px'>TapTrack Hub — SMTP Test</h2>"
+            "<p style='color:#334155'>This is a test email from <strong>TapTrack Hub</strong>.</p>"
+            "<p style='color:#334155'>If you received this, your SMTP configuration is working correctly.</p>"
+            "<p style='color:#94a3b8;font-size:12px;margin-top:24px'>TapTrack Hub Team</p>"
+            "</div>"
+        ),
+        email_type="test",
+    )
+
+    if success:
+        return {"message": f"Test email sent successfully to {body.to}"}
+    return {"message": "Failed to send test email — check SMTP configuration and server logs"}