Update generative models in various files

- Updated `ReviewScope.cs` to use `GenerativeModel.Gemini_20_Flash` instead of `GenerativeModel.Gemini_15_Flash`.
- Modified `SearchScope.cs` to use `GenerativeModel.Gemini_20_Flash_Lite` instead of the default model.
- Added new models to `GenerativeModel` enum in `GenerativeModel.cs`: `Gemini_20_Flash_Lite`, `Gemini_20_Flash`, and `Gemini_20_Flash_Thinking`.
- Updated `GenerateContent` method in `Generator.cs` to use `GenerativeModel.Gemini_20_Flash` by default.
- Updated `GenerateResponseForConversation` method in `Generator.cs` to use `GenerativeModel.Gemini_20_Flash_Lite` instead of `GenerativeModel.Gemini_15_Flash`.

Author: phanxuanquang

Diff for: Events/ReviewScope.cs

@@ -137,7 +137,7 @@ public static async Task<Comment> GenerateReview(string apiKey, EnglishLevel lev
             promptBuilder.AppendLine("## My writting for you to review: ");
             promptBuilder.AppendLine(content.Trim());
 
-            var result = await Generator.GenerateContent(apiKey, instructionBuilder.ToString(), promptBuilder.ToString(), true, 30, GenerativeModel.Gemini_15_Flash);
+            var result = await Generator.GenerateContent(apiKey, instructionBuilder.ToString(), promptBuilder.ToString(), true, 30, GenerativeModel.Gemini_20_Flash);
             return JsonConvert.DeserializeObject<Comment>(result);
         }
     }

Diff for: Events/SearchScope.cs

@@ -117,7 +117,7 @@ Người dùng có thể nhập vào từ hoặc cụm từ tiếng Anh để tr
                 promptBuilder.AppendLine($"- {context.Trim()}");
             }
 
-            return await Gemini.Generator.GenerateContent(apiKey, useEnglish ? instructionforEnglish : instructionforVietnamese, promptBuilder.ToString().Trim(), false, 50);
+            return await Gemini.Generator.GenerateContent(apiKey, useEnglish ? instructionforEnglish : instructionforVietnamese, promptBuilder.ToString().Trim(), false, 50, Gemini.GenerativeModel.Gemini_20_Flash_Lite);
         }
     }
 }

Diff for: Gemini/GenerativeModel.cs

@@ -12,5 +12,14 @@ public enum GenerativeModel
 
         [Description("gemini-1.5-flash-latest")]
         Gemini_15_Flash = 3,
+
+        [Description("gemini-2.0-flash-lite-preview-02-05")]
+        Gemini_20_Flash_Lite = 4,
+
+        [Description("gemini-2.0-flash")]
+        Gemini_20_Flash = 5,
+
+        [Description("gemini-2.0-flash-thinking-exp-01-21")]
+        Gemini_20_Flash_Thinking = 6,
     }
 }

Diff for: Gemini/Generator.cs

@@ -10,7 +10,7 @@ public static class Generator
     {
         private static readonly HttpClient Client = new();
 
-        public static async Task<string> GenerateContent(string apiKey, string? instruction, string query, bool useJson = true, double creativeLevel = 50, GenerativeModel model = GenerativeModel.Gemini_15_Flash)
+        public static async Task<string> GenerateContent(string apiKey, string? instruction, string query, bool useJson = true, double creativeLevel = 50, GenerativeModel model = GenerativeModel.Gemini_20_Flash)
         {
             var endpoint = GetUriWithHeadersIfAny(apiKey, model);
 
@@ -83,7 +83,7 @@ public static async Task<string> GenerateContent(string apiKey, string? instruct
 
         public static async Task<string> GenerateResponseForConversation(string apiKey, ChatRequest.Request requestData)
         {
-            var endpoint = GetUriWithHeadersIfAny(apiKey, GenerativeModel.Gemini_15_Flash);
+            var endpoint = GetUriWithHeadersIfAny(apiKey, GenerativeModel.Gemini_20_Flash_Lite);
 
             var body = new StringContent(JsonConvert.SerializeObject(requestData), Encoding.UTF8, "application/json");
             var response = await Client.PostAsync(endpoint, body);