docs: update Gemini model and enhance integration documentation

- Update Gemini model example from gemini-1.5-flash-latest to gemini-2.0-flash
- Add a Mermaid sequence diagram illustrating the interaction flow between the user, Gemini client, and Google GenAI API in Gemini integration documentation (including Chinese and Taiwanese localizations)

Signed-off-by: appleboy <[email protected]>

Author: appleboy

README.md

@@ -240,13 +240,30 @@ Build with the Gemini API, you can see the [Gemini API documentation][61]. Updat
 ```sh
 codegpt config set openai.provider gemini
 codegpt config set openai.api_key xxxxxxx
-codegpt config set openai.model gemini-1.5-flash-latest
+codegpt config set openai.model gemini-2.0-flash
 ```
 
 [60]: https://ai.google.dev/gemini-api
 [61]: https://ai.google.dev/gemini-api/docs
 [62]: https://aistudio.google.com/app/apikey
 
+```mermaid
+sequenceDiagram
+    participant User
+    participant GeminiClient as Gemini Provider
+    participant GenAI as Google GenAI API
+
+    User->>GeminiClient: Completion(ctx, content)
+    GeminiClient->>GenAI: GenerateContent(model, content, config)
+    GenAI-->>GeminiClient: Response (text, usage metadata)
+    GeminiClient-->>User: core.Response (text, usage)
+
+    User->>GeminiClient: GetSummaryPrefix(ctx, content)
+    GeminiClient->>GenAI: GenerateContent(model, content, config with function call)
+    GenAI-->>GeminiClient: Response (function call result)
+    GeminiClient-->>User: core.Response (prefix or error)
+```
+
 ### Support for [Anthropic][100] API Service
 
 Build with the Anthropic API, you can see the [Anthropic API documentation][101]. Update the `provider` and `api_key` in your config file. Please create an API key from the [Anthropic API][102] page.

README.zh-cn.md

@@ -228,7 +228,24 @@ codegpt config set openai.model xxxxx-gpt-4o
 ```sh
 codegpt config set openai.provider gemini
 codegpt config set openai.api_key xxxxxxx
-codegpt config set openai.model gemini-1.5-flash-latest
+codegpt config set openai.model gemini-2.0-flash
+```
+
+```mermaid
+sequenceDiagram
+    participant User
+    participant GeminiClient as Gemini Provider
+    participant GenAI as Google GenAI API
+
+    User->>GeminiClient: Completion(ctx, content)
+    GeminiClient->>GenAI: GenerateContent(model, content, config)
+    GenAI-->>GeminiClient: Response (text, usage metadata)
+    GeminiClient-->>User: core.Response (text, usage)
+
+    User->>GeminiClient: GetSummaryPrefix(ctx, content)
+    GeminiClient->>GenAI: GenerateContent(model, content, config with function call)
+    GenAI-->>GeminiClient: Response (function call result)
+    GeminiClient-->>User: core.Response (prefix or error)
 ```
 
 [60]: https://ai.google.dev/gemini-api

README.zh-tw.md

@@ -239,7 +239,24 @@ codegpt config set openai.model xxxxx-gpt-4o
 ```sh
 codegpt config set openai.provider gemini
 codegpt config set openai.api_key xxxxxxx
-codegpt config set openai.model gemini-1.5-flash-latest
+codegpt config set openai.model gemini-2.0-flash
+```
+
+```mermaid
+sequenceDiagram
+    participant User
+    participant GeminiClient as Gemini Provider
+    participant GenAI as Google GenAI API
+
+    User->>GeminiClient: Completion(ctx, content)
+    GeminiClient->>GenAI: GenerateContent(model, content, config)
+    GenAI-->>GeminiClient: Response (text, usage metadata)
+    GeminiClient-->>User: core.Response (text, usage)
+
+    User->>GeminiClient: GetSummaryPrefix(ctx, content)
+    GeminiClient->>GenAI: GenerateContent(model, content, config with function call)
+    GenAI-->>GeminiClient: Response (function call result)
+    GeminiClient-->>User: core.Response (prefix or error)
 ```
 
 [60]: https://ai.google.dev/gemini-api