feat: report the source export timestamp on every travel export page

tests/Service/TravelExportBuilderTest.php

@@ -156,6 +156,18 @@ class TravelExportBuilderTest extends TestCase
     /**
      * @return array<string, mixed>
      */
+    public function testCarriesTheSourceExportTimestamp(): void
+    {
+        $export = $this->build(null, ['Ziel_1.xml'], "22.09.2026 11:10:15\r\nLetzte \xDCbertragung\r\nAnzahl \xDCbertragene Dateien: 177\r\nVollexport\r\n");
+
+        self::assertSame('2026-09-22T11:10:15+02:00', $export->sourceGeneratedAt?->format('c'));
+    }
+
+    public function testTheSourceExportTimestampIsNullWithoutAMarker(): void
+    {
+        self::assertNull($this->build()->sourceGeneratedAt);
+    }
+
     private function rowFor(string $key): array
     {
         foreach ($this->build()->rows as $row) {
@@ -170,7 +182,7 @@ class TravelExportBuilderTest extends TestCase
     /**
      * @param list<string> $files
      */
-    private function build(?string $xml = null, array $files = ['Ziel_1.xml']): TravelExport
+    private function build(?string $xml = null, array $files = ['Ziel_1.xml'], ?string $marker = null): TravelExport
     {
         $contents = [
             'Ziel_1.xml' => $xml ?? (string) file_get_contents(__DIR__.'/../Resources/travel_export_data.xml'),
@@ -183,7 +195,10 @@ class TravelExportBuilderTest extends TestCase
             $files,
         )));
         $filesystem->method('read')->willReturnCallback(
-            static fn (string $path): string => $contents[$path] ?? ''
+            static fn (string $path): string => 'uebertragung.info' === $path ? (string) $marker : $contents[$path] ?? ''
+        );
+        $filesystem->method('fileExists')->willReturnCallback(
+            static fn (string $path): bool => 'uebertragung.info' === $path && null !== $marker
         );
 
         $hotelLoader = $this->createStub(HotelLoader::class);