fix: Email template improvements

backend/src/features/notifications/migrations/005_update_email_templates_html.sql

@@ -0,0 +1,16 @@
+/**
+ * Migration: Add HTML body column to email templates
+ * @ai-summary Non-breaking migration for future HTML template support
+ * @ai-context Existing plain text templates auto-convert to HTML
+ */
+
+-- Add optional html_body column for custom HTML templates (future enhancement)
+ALTER TABLE email_templates
+ADD COLUMN html_body TEXT DEFAULT NULL;
+
+-- Add comment explaining the column purpose
+COMMENT ON COLUMN email_templates.html_body IS
+  'Optional custom HTML body. If NULL, the plain text body will be auto-converted to HTML with base layout.';
+
+-- No data updates needed - existing templates continue to work
+-- The system will auto-convert plain text body to HTML using renderEmailHtml()