fix: Handle duplicate email in createUcastnik

If participant with same email exists, update their data and
return existing record instead of throwing duplicate key error.

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

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

@@ -45,6 +45,40 @@ export const getUcastnikById = async (id) => {
 };
 
 export const createUcastnik = async (data) => {
+  // Check if participant with this email already exists
+  if (data.email) {
+    const [existing] = await db
+      .select()
+      .from(ucastnici)
+      .where(eq(ucastnici.email, data.email))
+      .limit(1);
+
+    if (existing) {
+      // Update existing participant with new data and return
+      const [updated] = await db
+        .update(ucastnici)
+        .set({
+          titul: data.titul || existing.titul,
+          meno: data.meno || existing.meno,
+          priezvisko: data.priezvisko || existing.priezvisko,
+          telefon: data.telefon || existing.telefon,
+          firma: data.firma || existing.firma,
+          firmaIco: data.firmaIco || existing.firmaIco,
+          firmaDic: data.firmaDic || existing.firmaDic,
+          firmaIcDph: data.firmaIcDph || existing.firmaIcDph,
+          firmaSidlo: data.firmaSidlo || existing.firmaSidlo,
+          mesto: data.mesto || existing.mesto,
+          ulica: data.ulica || existing.ulica,
+          psc: data.psc || existing.psc,
+          updatedAt: new Date(),
+        })
+        .where(eq(ucastnici.id, existing.id))
+        .returning();
+
+      return updated;
+    }
+  }
+
   const [newUcastnik] = await db
     .insert(ucastnici)
     .values({