Add CONTRIBUTING.md and AGENTS.md

[fcostaoliveira]

Summary

• Adds baseline CONTRIBUTING.md (project setup, coding standards, PR workflow, testing, review process)
• Adds AGENTS.md with AI agent guidelines

Part of the Redis "Open Source within Redis" initiative — ensuring every repo in the org has clear contribution and agent guidelines to enable cross-team contributions.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 47.53%. Comparing base (12b11f1) to head (00560f0).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #543      +/-   ##
==========================================
+ Coverage   47.50%   47.53%   +0.03%     
==========================================
  Files          74       74              
  Lines        8907     8907              
==========================================
+ Hits         4231     4234       +3     
+ Misses       4676     4673       -3     

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