Replace Mermaid diagrams with images to enhance documentation quality

[lanshi17]

This pull request updates both the English and Chinese documentation to replace all embedded Mermaid diagrams with static image files for improved rendering and portability. The diagrams illustrating core concepts in the dialog loop, message types, tool system, and state machines are now referenced as local image assets, with descriptive alt text provided for accessibility.

Documentation Diagram Updates:

Dialog Loop and State Machine Visualizations:

• Replaced Mermaid diagrams with image references in the English documentation (en/Part-1-Foundations/02-The-Dialog-Loop-Heartbeat-of-an-Agent.md), including diagrams for async generators, message types, dialog loop flow, termination reasons, and state transitions. [1] [2] [3] [4] [5]
• Made corresponding replacements in the Chinese documentation (第一部分-基础篇/02-对话循环-Agent的心跳.md), ensuring all Mermaid diagrams are replaced with appropriate image files and localized alt text. [1] [2] [3] [4] [5]

Tool System and Execution Flow:

• Updated tool batching and execution timeline diagrams in the English tool system documentation (en/Part-1-Foundations/03-The-Tool-System-Agent-Hands.md) to use static images instead of Mermaid. [1] [2]
• Applied the same updates to the Chinese tool system documentation (第一部分-基础篇/03-工具系统-Agent的双手.md). [1] [2]

These changes ensure consistent, reliable display of diagrams across platforms and improve the accessibility and maintainability of the documentation.