[codex] Distributed lock interview notes

[loulanyue]

Summary

• Add distributed lock guidance covering Redis locks, Redisson, ZooKeeper locks, selection tradeoffs, and idempotency fallback.
• Keep the content aligned with agent_java_offer's backend interview focus while preserving interview-notes structure.

Target file

• 05-system-design/distributed/9.分布式锁.md

Validation

• node scripts/run-maintenance-checks.mjs

Closes #106