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>

src/lib/email.ts

@@ -336,7 +336,7 @@ function statCard(label: string, value: string | number): string {
 // Email Templates
 // =============================================================================
 
-interface EmailTemplate {
+export interface EmailTemplate {
   subject: string
   html: string
   text: string
@@ -2689,6 +2689,23 @@ export const NOTIFICATION_EMAIL_TEMPLATES: Record<string, TemplateGenerator> = {
     ),
 }
 
+/**
+ * Resolve the email template for a notification type without sending.
+ * Exported for use by preview endpoints.
+ */
+export function renderNotificationEmail(
+  name: string,
+  type: string,
+  context: NotificationEmailContext,
+  subjectOverride?: string,
+): EmailTemplate {
+  const generator = NOTIFICATION_EMAIL_TEMPLATES[type]
+  const template = generator
+    ? generator({ ...context, linkUrl: ensureAbsoluteUrl(context.linkUrl), name })
+    : getNotificationEmailTemplate(name, subjectOverride || context.title, context.message, ensureAbsoluteUrl(context.linkUrl))
+  return subjectOverride ? { ...template, subject: subjectOverride } : template
+}
+
 /**
  * Send styled notification email using the appropriate template
  */
@@ -2699,32 +2716,7 @@ export async function sendStyledNotificationEmail(
   context: NotificationEmailContext,
   subjectOverride?: string
 ): Promise<void> {
-  // Safety net: always ensure linkUrl is absolute before passing to templates
-  const safeContext = {
-    ...context,
-    linkUrl: ensureAbsoluteUrl(context.linkUrl),
-  }
-  const templateGenerator = NOTIFICATION_EMAIL_TEMPLATES[type]
-
-  let template: EmailTemplate
-
-  if (templateGenerator) {
-    // Use styled template
-    template = templateGenerator({ ...safeContext, name })
-    // Apply subject override if provided
-    if (subjectOverride) {
-      template.subject = subjectOverride
-    }
-  } else {
-    // Fall back to generic template
-    template = getNotificationEmailTemplate(
-      name,
-      subjectOverride || safeContext.title,
-      safeContext.message,
-      safeContext.linkUrl
-    )
-  }
-
+  const template = renderNotificationEmail(name, type, context, subjectOverride)
   await sendEmail({ to: email, subject: template.subject, text: template.text, html: template.html })
 }