feat(project): persist catalog snapshot in project data

lib/project_codec.dart

@@ -1,6 +1,28 @@
 import 'dart:convert';
 import 'dart:typed_data';
 
+class MosaicPaletteSnapshotEntry {
+  final String name;
+  final int colorValue;
+
+  const MosaicPaletteSnapshotEntry({
+    required this.name,
+    required this.colorValue,
+  });
+
+  Map<String, dynamic> toJson() => {
+        'name': name,
+        'colorValue': colorValue,
+      };
+
+  factory MosaicPaletteSnapshotEntry.fromJson(Map<String, dynamic> json) {
+    return MosaicPaletteSnapshotEntry(
+      name: json['name'] as String? ?? 'Unbenannt',
+      colorValue: (json['colorValue'] as num?)?.toInt() ?? 0xFF000000,
+    );
+  }
+}
+
 class MosaicProjectData {
   final bool useCapSize;
   final String gridWidth;
@@ -12,6 +34,7 @@ class MosaicProjectData {
   final double colorVariation;
   final String selectedPreset;
   final Uint8List? sourceImageBytes;
+  final List<MosaicPaletteSnapshotEntry> catalogSnapshot;
   final DateTime savedAt;
 
   const MosaicProjectData({
@@ -25,6 +48,7 @@ class MosaicProjectData {
     required this.colorVariation,
     required this.selectedPreset,
     required this.sourceImageBytes,
+    required this.catalogSnapshot,
     required this.savedAt,
   });
 
@@ -40,23 +64,32 @@ class MosaicProjectData {
         'selectedPreset': selectedPreset,
         'sourceImageBase64':
             sourceImageBytes == null ? null : base64Encode(sourceImageBytes!),
+        'catalogSnapshot': catalogSnapshot.map((entry) => entry.toJson()).toList(),
         'savedAt': savedAt.toIso8601String(),
       };
 
   factory MosaicProjectData.fromJson(Map<String, dynamic> json) {
     final sourceB64 = json['sourceImageBase64'] as String?;
+    final snapshotRaw = (json['catalogSnapshot'] as List?) ?? const [];
     return MosaicProjectData(
       useCapSize: json['useCapSize'] as bool? ?? false,
       gridWidth: json['gridWidth'] as String? ?? '40',
       gridHeight: json['gridHeight'] as String? ?? '30',
       capSize: json['capSize'] as String? ?? '12',
       fidelityStructure: (json['fidelityStructure'] as num?)?.toDouble() ?? 0.5,
-      ditheringStrength: (json['ditheringStrength'] as num?)?.toDouble() ?? 0.35,
+      ditheringStrength:
+          (json['ditheringStrength'] as num?)?.toDouble() ?? 0.35,
       edgeEmphasis: (json['edgeEmphasis'] as num?)?.toDouble() ?? 0.4,
       colorVariation: (json['colorVariation'] as num?)?.toDouble() ?? 0.3,
       selectedPreset: json['selectedPreset'] as String? ?? 'ausgewogen',
       sourceImageBytes: sourceB64 == null ? null : base64Decode(sourceB64),
-      savedAt: DateTime.tryParse(json['savedAt'] as String? ?? '') ?? DateTime.now(),
+      catalogSnapshot: snapshotRaw
+          .whereType<Map>()
+          .map((entry) => MosaicPaletteSnapshotEntry.fromJson(
+              Map<String, dynamic>.from(entry)))
+          .toList(growable: false),
+      savedAt:
+          DateTime.tryParse(json['savedAt'] as String? ?? '') ?? DateTime.now(),
     );
   }
 }