fix: upgrade diagnostic logs to info level for production visibility

[lishuceo]

Summary

• 将 PR chore: add diagnostic logging for history dedup pipeline #140 中的诊断日志从 logger.debug 改为 logger.info
• 生产环境 LOG_LEVEL=info，debug 日志不可见

影响范围

三处诊断日志：fetchRecentMessages、buildDirectTaskHistory、executeDirectTask

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[claude]

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Review: PR #141 — Upgrade diagnostic logs to info level

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✅ Approved — Clean, minimal change. No issues found.

This PR correctly upgrades all 5 diagnostic log statements added in PR #140 from logger.debug to logger.info. Since production runs with LOG_LEVEL=info, the debug-level logs were invisible in production — this fix ensures the diagnostic data is actually observable where it matters.

Files reviewed:

• src/feishu/client.ts — 1 log in fetchRecentMessages
• src/feishu/event-handler.ts — 4 logs across executeDirectTask and buildDirectTaskHistory

Notes:

• These diagnostic logs include potentially verbose data (message ID arrays, content lengths). This is fine for temporary debugging, but consider reverting to debug level or removing them once the history dedup pipeline is confirmed stable in production.