feat: colored tag categories division like e621/gelbooru/rule34 and fix search for tags with parentheses

lib/backend/providers/provider_manager.dart

@@ -169,7 +169,16 @@ class ProviderManager {
 
     for (final raw in rawTags) {
       var token = raw.trim();
-      token = token.replaceAll(RegExp(r'^[\(\)]+|[\(\)]+$'), '').trim();
+      if (token.isEmpty) continue;
+
+      // Only strip parentheses if they are grouping delimiters (unbalanced in the token, e.g. '(cat' or 'dog)')
+      // but preserve tags that have internal paired parentheses like 'tyson_(password)'.
+      if (token.startsWith('(') && !token.contains(')')) {
+        token = token.substring(1).trim();
+      }
+      if (token.endsWith(')') && !token.contains('(')) {
+        token = token.substring(0, token.length - 1).trim();
+      }
       if (token.isEmpty) continue;
 
       if (token.toLowerCase() == 'and') {

lib/backend/services/search_service.dart

@@ -21,10 +21,7 @@ class SearchService {
   TagCacheService? get tagCacheService => _tagCacheService;
 
   static String sanitizeToken(String raw) {
-    return raw
-        .replaceAll(RegExp(r'^[\(\)]+|[\(\)]+$'), '')
-        .trim()
-        .toLowerCase();
+    return raw.trim().toLowerCase();
   }
 
   List<String> parseTags(String query) {

lib/backend/services/tag_cache_service.dart

@@ -66,10 +66,11 @@ class TagCacheService {
     int limit = 16,
     Iterable<String>? priorityTags,
   }) {
-    final cleanPrefix = prefix
-        .replaceAll(RegExp(r'^[\(\)]+|[\(\)]+$'), '')
-        .trim()
-        .toLowerCase();
+    var cleanPrefix = prefix.trim().toLowerCase();
+    // If the prefix has an unbalanced opening parenthesis at the start (e.g. '(cat'), strip it
+    if (cleanPrefix.startsWith('(') && !cleanPrefix.contains(')')) {
+      cleanPrefix = cleanPrefix.substring(1).trim();
+    }
     if (cleanPrefix.isEmpty) return const [];
 
     final prioritySet = priorityTags