feat: create Mailjet lists for travel mailings

tests/Service/TravelIndexTest.php

@@ -186,6 +186,32 @@ class TravelIndexTest extends TestCase
         $this->assertNull($result);
     }
 
+    // -------------------------------------------------------------------------
+    // mapDateCodeToStartDate
+    // -------------------------------------------------------------------------
+
+    public function testMapDateCodeToStartDateReturnsTheTravelStartDate(): void
+    {
+        $this->travelLoader->method('generateFilesMap')->willReturn([
+            42 => ['id' => 42, 'code' => 'WI25', 'dateFrom' => new \DateTimeImmutable('2026-12-28'), 'hotels' => []],
+        ]);
+        $this->travelSnapshotService->method('generateMapping')->willReturn([]);
+
+        $result = $this->service()->mapDateCodeToStartDate('WI25');
+
+        $this->assertEquals(new \DateTimeImmutable('2026-12-28'), $result);
+    }
+
+    public function testMapDateCodeToStartDateReturnsNullWhenNotFound(): void
+    {
+        $this->travelLoader->method('generateFilesMap')->willReturn([]);
+        $this->travelSnapshotService->method('generateMapping')->willReturn([]);
+
+        $result = $this->service()->mapDateCodeToStartDate('UNKNOWN');
+
+        $this->assertNull($result);
+    }
+
     // -------------------------------------------------------------------------
     // mapHotelCodeToId
     // -------------------------------------------------------------------------