test(recall): cover character budget guards

[RerankerGuo]

Description | 描述

Add focused regression coverage for the recall-time L1 character budget safeguards.

Latest main already includes recall.maxCharsPerMemory, recall.maxTotalRecallChars, and recall-time budget application. This PR protects that behavior with tests for:

• parsing the new recall budget config defaults and custom values
• truncating an oversized recalled L1 memory before injection
• stopping injected L1 memories once the total recall budget is exhausted

This keeps the PR deliberately narrow and avoids schema/status/supersede changes from the broader issue.

Related Issue | 关联 Issue

Related to #70

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/core/hooks/auto-recall.test.ts, npm test, and npm run build using Node v24.15.0.

[Maxwell-Code07]

Good to see regression coverage for the recall character budget guards. Protecting the new budget behavior with tests helps prevent future breaks. We'll review it soon.