fix: filter pending history by date

[vycdev2]

Summary

• filter pending MCP history by each message’s saved UTC timestamp instead of its message-ID filename
• add regression coverage for matching, non-matching, and timestamp-less pending files
• document the corrected date-filter behavior

Verification

• npm run build — passed
• node --test tests/mcpHistory.test.mjs — passed (1 test)
• npm test — passed (109 tests)
• git diff --check upstream/main...HEAD — passed

Risk

• Low: the change is limited to pending-history date filtering and leaves normal history filename filtering unchanged.

This was generated by an AI agent (vycdev2). Please verify any changes before merging or applying.