Add provider tag suggestions and tag categories

lib/backend/models/post.dart

@@ -14,6 +14,7 @@ class Post {
     required this.createdAt,
     required this.fileType,
     required this.score,
+    this.tagGroups = const {},
   });
 
   final String id;
@@ -30,6 +31,7 @@ class Post {
   final DateTime createdAt;
   final String fileType;
   final int score;
+  final Map<String, List<String>> tagGroups;
 
   String get cacheKey => '$providerId:$id';
 
@@ -48,6 +50,7 @@ class Post {
         'createdAt': createdAt.toIso8601String(),
         'fileType': fileType,
         'score': score,
+        'tagGroups': tagGroups,
       };
 
   factory Post.fromJson(Map<String, dynamic> json) => Post(
@@ -66,5 +69,12 @@ class Post {
             DateTime.fromMillisecondsSinceEpoch(0),
         fileType: (json['fileType'] as String?) ?? 'unknown',
         score: (json['score'] as num?)?.toInt() ?? 0,
+        tagGroups: (json['tagGroups'] as Map?)?.map(
+              (key, value) => MapEntry(
+                key.toString(),
+                List<String>.from((value as List?) ?? const []),
+              ),
+            ) ??
+            const {},
       );
 }

lib/backend/models/tag_suggestion.dart

@@ -0,0 +1,38 @@
+enum TagCategory {
+  general,
+  artist,
+  copyright,
+  character,
+  meta,
+  species,
+  unknown,
+}
+
+class TagSuggestion {
+  const TagSuggestion({
+    required this.name,
+    required this.category,
+    required this.postCount,
+    required this.providerId,
+  });
+
+  final String name;
+  final TagCategory category;
+  final int postCount;
+  final String providerId;
+
+  String get categoryLabel => category.name;
+}
+
+TagCategory tagCategoryFromString(String? value) {
+  final normalized = (value ?? '').toLowerCase();
+  return switch (normalized) {
+    '0' || 'general' => TagCategory.general,
+    '1' || 'artist' => TagCategory.artist,
+    '3' || 'copyright' || 'circle' => TagCategory.copyright,
+    '4' || 'character' => TagCategory.character,
+    '5' || 'meta' || 'metadata' => TagCategory.meta,
+    'species' => TagCategory.species,
+    _ => TagCategory.unknown,
+  };
+}