feat(recall): add injected context visibility option

[RerankerGuo]

Description | 描述

Add recall.showInjected so users can opt into preserving auto-recall context in conversation history for transparency.

• Parses recall.showInjected with a backward-compatible default of false.
• Keeps existing transcript cleanup behavior by default, but skips stripping injected recall context when enabled.
• Moves recall stripping into a small tested helper and documents the option in plugin schema and README files.

Related Issue | 关联 Issue

Fix #114

Change Type | 修改类型

• Bug fix | Bug 修复
• New feature | 新功能
• Documentation update | 文档更新
• Code optimization | 代码优化

Self-test Checklist | 自测清单

• Verified locally | 本地验证通过
• No existing features affected | 无影响现有功能

Additional Notes | 其他说明

Verified with npx vitest run src/config.test.ts src/utils/recall-injection.test.ts, npm test, and npm run build using Node v24.15.0.

[Maxwell-Code07]

Adding user control over injected context visibility is a thoughtful enhancement. The backward-compatible default keeps existing behavior unchanged. We'll review it and get back to you.