[BUILD] Add AGENTS.md

[Zouxxyy]

Purpose

AI agents are already everywhere; it’s time to start writing AGENTS.md (Partly based on Apache Spark's AGENTS.md).

Tests

On my Mac, have the AI agent change a single line in a file under paimon-api module, then run the test, cost 4.999 s

mvn test -Dcheckstyle.skip -Dspotless.check.skip -Denforcer.skip -DfailIfNoTests=false  \
-pl paimon-spark/paimon-spark-common -am \
-Dtest='CatalogUtilsTest'

[INFO] Tests run: 2, Failures: 0, Errors: 0, Skipped: 0
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  4.999 s (Wall Clock)
[INFO] ------------------------------------------------------------------------

Without skip options, cost 15.075 s

mvn test -DfailIfNoTests=false  \
-pl paimon-spark/paimon-spark-common -am \
-Dtest='CatalogUtilsTest'

[INFO] Tests run: 2, Failures: 0, Errors: 0, Skipped: 0
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  15.075 s (Wall Clock)
[INFO] ------------------------------------------------------------------------

API and Format

Documentation

Generative AI tooling

Generated-by: Qoder and gpt-5.2