feat(notifications): renderNotificationEmail + previewEmailTemplate + logistics sample data

- Export `renderNotificationEmail` from email.ts (pure template resolver, no send)
- Refactor `sendStyledNotificationEmail` to delegate to `renderNotificationEmail`
- Hoist sampleData to module-level `NOTIFICATION_SAMPLE_DATA` in notification router
- Add 8 logistics sample entries (FINALIST_*/TRAVEL_CONFIRMED/VISA_STATUS_UPDATE)
- Add `notification.previewEmailTemplate` adminProcedure query (returns subject/html/hasStyledTemplate)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/unit/notification-preview.test.ts

@@ -0,0 +1,62 @@
+/**
+ * Task 1: renderNotificationEmail + previewEmailTemplate
+ *
+ * Tests that:
+ * 1. previewEmailTemplate returns rendered HTML and a non-empty subject for a
+ *    type that has a styled template (VISA_STATUS_UPDATE).
+ * 2. previewEmailTemplate returns non-empty HTML for a fallback type
+ *    (FINALIST_EXPIRED — no registered template, uses generic fallback).
+ */
+import { afterAll, describe, expect, it } from 'vitest'
+import { createCaller, prisma } from '../setup'
+import { createTestUser, cleanupTestData, uid } from '../helpers'
+import { notificationRouter } from '../../src/server/routers/notification'
+
+describe('notification.previewEmailTemplate', () => {
+  let adminId: string
+  let adminEmail: string
+
+  afterAll(async () => {
+    if (adminId) {
+      await prisma.user.deleteMany({ where: { id: adminId } })
+    }
+  })
+
+  async function getAdminCaller() {
+    if (!adminId) {
+      const admin = await createTestUser('SUPER_ADMIN', {
+        name: 'Preview Admin',
+        email: `preview-admin-${uid()}@test.local`,
+      })
+      adminId = admin.id
+      adminEmail = admin.email
+    }
+    return createCaller(notificationRouter, {
+      id: adminId,
+      email: adminEmail,
+      name: 'Preview Admin',
+      role: 'SUPER_ADMIN',
+    })
+  }
+
+  it('returns HTML containing a visa-related string and a non-empty subject for VISA_STATUS_UPDATE', async () => {
+    const caller = await getAdminCaller()
+    const result = await caller.previewEmailTemplate({ notificationType: 'VISA_STATUS_UPDATE' })
+
+    expect(result.subject).toBeTruthy()
+    expect(result.html).toBeTruthy()
+    // The visa template includes 'visa' or 'Grand' in its content
+    const lower = result.html.toLowerCase()
+    expect(lower.includes('visa') || lower.includes('grand')).toBe(true)
+    expect(result.hasStyledTemplate).toBe(true)
+  })
+
+  it('returns non-empty HTML for FINALIST_EXPIRED (fallback — no styled template)', async () => {
+    const caller = await getAdminCaller()
+    const result = await caller.previewEmailTemplate({ notificationType: 'FINALIST_EXPIRED' })
+
+    expect(result.html).toBeTruthy()
+    expect(result.subject).toBeTruthy()
+    expect(result.hasStyledTemplate).toBe(false)
+  })
+})