* refactor: streamline system prompt handling and introduce built-in tools
- Removed the static SYSTEM_PROMPT_THRESHOLD from BaseApiClient and replaced it with a constant in constant.ts.
- Updated API clients (AnthropicAPIClient, GeminiAPIClient, OpenAIApiClient, OpenAIResponseAPIClient) to simplify system prompt logic by eliminating unnecessary checks and using new utility functions for prompt building.
- Introduced built-in tools functionality, including a new 'think' tool, to enhance the tool usage experience.
- Refactored ApiService to integrate built-in tools and adjust system prompt modifications accordingly.
- Added utility functions for managing built-in tools in mcp-tools.ts and created a new tools index for better organization.
* refactor(tests): update prompt tests to use new buildSystemPromptWithTools function
- Renamed the function used in prompt tests from buildSystemPrompt to buildSystemPromptWithTools to reflect recent changes in prompt handling.
- Adjusted test cases to ensure compatibility with the updated function, maintaining the integrity of user prompt handling.
* refactor(ApiService, mcp-tools, prompt): enhance tool usage and prompt handling
- Updated ApiService to improve system prompt construction based on tool usage mode, ensuring clearer logic for tool integration.
- Enhanced mcp-tools with a new response structure for the 'think' tool, allowing for better handling of tool responses.
- Expanded prompt utility functions to include detailed instructions for using the 'think' tool, improving user guidance.
- Refactored tests to validate new prompt building logic and tool integration, ensuring robust functionality across scenarios.
* fix: enhance prompt
* feat(McpToolChunkMiddleware): enhance tool call handling with built-in tool support
- Added support for built-in tools in the parseAndCallTools function, allowing for conditional tool invocation based on tool type.
- Implemented a check to return early if the tool call response is null, improving error handling.
