[Feature]: Optimize system notification content

[snowjuly]

Problem statement

The current system notification content contains original markdown format, it needs to be changed to plain text summary content to avoid confusion

Proposed solution

粘贴文本
System notifications changed to pure text summary content, avoid confusion

Alternatives considered

No response

Main area

frontend

Risk boundaries

• AgentService or conversation runtime
• tool execution or instruction loading
• session persistence or context construction
• MCP integration
• database schema or migrations

Mockups, screenshots, or examples

No response