load trending images from tmdb at startup

- need TMDB_API_KEY as environment variable
- mount /cache for data persistence

Signed-off-by: Peter Siegmund <developer@mars3142.org>

server/cinema/lib/common/domain/custom_date_time_serializer.dart

@@ -0,0 +1,32 @@
+import 'package:built_value/serializer.dart';
+
+/// A custom serializer for [DateTime] objects that are represented as
+/// a simple date string "yyyy-MM-dd" in JSON.
+class CustomDateTimeSerializer implements PrimitiveSerializer<DateTime> {
+  @override
+  final Iterable<Type> types = const [DateTime];
+
+  @override
+  final String wireName = 'DateTime';
+
+  @override
+  Object serialize(Serializers serializers, DateTime dateTime,
+      {FullType specifiedType = FullType.unspecified}) {
+    // On serialization, convert DateTime to a "yyyy-MM-dd" string.
+    return dateTime.toIso8601String().substring(0, 10);
+  }
+
+  @override
+  DateTime deserialize(Serializers serializers, Object serialized,
+      {FullType specifiedType = FullType.unspecified}) {
+    // On deserialization, parse the string to a DateTime object.
+    // This handles formats like "2025-09-23".
+    final parts = (serialized as String).split('-');
+    final dateUtc = DateTime.utc(
+      int.parse(parts[0]),
+      int.parse(parts[1]),
+      int.parse(parts[2]),
+    );
+    return dateUtc;
+  }
+}

server/cinema/lib/common/domain/serializers.dart

@@ -0,0 +1,20 @@
+import 'package:built_collection/built_collection.dart';
+import 'package:built_value/serializer.dart';
+import 'package:built_value/standard_json_plugin.dart';
+import 'package:cinema/feature/poster/domain/movie.dart';
+import 'package:cinema/feature/poster/domain/tmdb_trending_response.dart';
+
+import 'custom_date_time_serializer.dart';
+
+part 'serializers.g.dart';
+
+@SerializersFor([TmdbTrendingResponse, TmdbMovieResult])
+final Serializers serializers =
+    (_$serializers.toBuilder()
+          ..add(CustomDateTimeSerializer())
+          ..addPlugin(StandardJsonPlugin())
+          ..addBuilderFactory(
+            const FullType(BuiltList, [FullType(TmdbMovieResult), FullType(Movie)]),
+            () => ListBuilder<TmdbMovieResult>(),
+          ))
+        .build();