refactor: Move course dates from registracie to kurzy table

- Add datumOd and datumDo columns to kurzy table
- Remove datumOd, datumDo, pocetUcastnikov from registracie table
- Update schema, validators, and services accordingly
- Certificate generation now uses course dates
- Migration preserves existing data by copying most recent dates

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/services/ai-kurzy/certificate.service.js

@@ -151,8 +151,6 @@ export const generateCertificate = async (registraciaId, templateName = 'AIcerti
   const [registration] = await db
     .select({
       id: registracie.id,
-      datumOd: registracie.datumOd,
-      datumDo: registracie.datumDo,
       ucastnikId: registracie.ucastnikId,
       kurzId: registracie.kurzId,
     })
@@ -184,6 +182,8 @@ export const generateCertificate = async (registraciaId, templateName = 'AIcerti
     .select({
       nazov: kurzy.nazov,
       popis: kurzy.popis,
+      datumOd: kurzy.datumOd,
+      datumDo: kurzy.datumDo,
     })
     .from(kurzy)
     .where(eq(kurzy.id, registration.kurzId))
@@ -205,16 +205,16 @@ export const generateCertificate = async (registraciaId, templateName = 'AIcerti
     .filter(Boolean)
     .join(' ');
 
-  const issueDate = registration.datumDo || registration.datumOd || new Date();
+  const issueDate = course.datumDo || course.datumOd || new Date();
 
   // Format date range
   let dateRange = '';
-  if (registration.datumOd && registration.datumDo) {
-    dateRange = `${formatDate(registration.datumOd)} - ${formatDate(registration.datumDo)}`;
-  } else if (registration.datumDo) {
-    dateRange = formatDate(registration.datumDo);
-  } else if (registration.datumOd) {
-    dateRange = formatDate(registration.datumOd);
+  if (course.datumOd && course.datumDo) {
+    dateRange = `${formatDate(course.datumOd)} - ${formatDate(course.datumDo)}`;
+  } else if (course.datumDo) {
+    dateRange = formatDate(course.datumDo);
+  } else if (course.datumOd) {
+    dateRange = formatDate(course.datumOd);
   }
 
   // Prepare template data