fix(crm): pre-event reminder passes raw event_date (fixes "Invalid Date" in the email)

composePayload pre-formatted event_date to DD.MM.YYYY, but emailProcessor runs
date variables through formatDate(value, language) — new Date("25.06.2026")
can't parse → the email rendered "Invalid Date". Pass the raw event_date and let
the processor localise it, matching the expiry mailer's contract. Pre-existing
in the migration-143 composePayload (dormant while the legacy pass was gated
off); surfaced once the pre_event_email flow ran.

backend/src/services/eventReminderService.js

@@ -103,18 +103,14 @@ function composePayload({ event, recipientEmail, daysBefore, businessName }) {
     || event.host_name
     || recipientEmail
     || '';
-  // Event date formatted DD.MM.YYYY here for simplicity; the rendered
-  // email may further re-locale via the template engine when locale-
-  // aware formatters are introduced.
-  const ed = event.event_date instanceof Date ? event.event_date : new Date(event.event_date);
-  const day = String(ed.getUTCDate()).padStart(2, '0');
-  const month = String(ed.getUTCMonth() + 1).padStart(2, '0');
-  const year = ed.getUTCFullYear();
-  const eventDateFormatted = `${day}.${month}.${year}`;
+  // Pass the RAW event_date — emailProcessor.processTemplate runs it through
+  // formatDate(value, recipientLanguage). Pre-formatting it (e.g. DD.MM.YYYY)
+  // makes the processor's new Date(...) reparse fail → "Invalid Date". Same
+  // contract the expiry mailer uses.
   return {
     customer_name: customerName,
     event_name: event.event_name || `Event #${event.id}`,
-    event_date: eventDateFormatted,
+    event_date: event.event_date || '',
     event_type: event.event_type || '',
     days_before: daysBefore,
     business_name: businessName || '',