fix(memos-local-openclaw): sanitize captured metadata and evidence

[ai-jiaqian]

Description

This PR fixes memory capture sanitization issues in the local OpenClaw memos plugin.

Problem:

• User messages with OpenClaw envelope timestamps were only sanitized when the timestamp started at column 0, so messages with leading whitespace kept the timestamp prefix in stored memory.
• Assistant messages containing explicit [STORED_MEMORY]...[/STORED_MEMORY] evidence blocks were re-ingested verbatim, causing evidence anti-writeback failures and polluting stored memories.
• The capture path needed to preserve ordinary mentions of the evidence tag while stripping only explicit wrapper blocks.

Changes:

• Normalize inbound timestamp stripping so envelope prefixes are removed even when preceded by whitespace.
• Reuse the configured evidenceWrapperTag during capture and remove explicit evidence wrapper blocks from assistant/tool text before storage.
• Keep ordinary plain-text mentions of STORED_MEMORY unchanged.
• Add regression coverage for timestamp sanitization and evidence anti-writeback behavior.

Relevant context:

• No additional dependencies are required.

Related Issue (Required): N/A

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (does not change functionality, e.g. code style improvements, linting)
• Documentation update

How Has This Been Tested?

• Unit Test
• Test Script Or Test Steps (please provide)
• Pipeline Automated API Test (please provide)

Test command run:

• npm test -- --run tests/capture.test.ts tests/integration.test.ts

Checklist

• I have performed a self-review of my own code | 我已自行检查了自己的代码
• I have commented my code in hard-to-understand areas | 我已在难以理解的地方对代码进行了注释
• I have added tests that prove my fix is effective or that my feature works | 我已添加测试以证明我的修复有效或功能正常
• I have created related documentation issue/PR in MemOS-Docs (if applicable) | 我已在 MemOS-Docs 中创建了相关的文档 issue/PR（如果适用）
• I have linked the issue to this PR (if applicable) | 我已将 issue 链接到此 PR（如果适用）
• I have mentioned the person who will review this PR | 我已提及将审查此 PR 的人