Add repo-local AGENTS.md with deterministic validation workflow guidance

[davidahmann]

Contributors and automation agents lack a single machine-readable instruction file, leading to inconsistent local validation and avoidable PR churn.

Current behavior is insufficient because there is no repo-local AGENTS.md to codify deterministic validation, safety boundaries, and contribution workflow expectations.

Why now: cross-repo orchestration assumes repo-local guidance parity and this repo currently diverges.

Claim-to-codepath map:

• Contributor guidance surface in README.md and contributing docs.
• Validation workflow expectations for lib/crewai test/lint/format paths.

Requested behavior: introduce a repo-local AGENTS.md with explicit validation commands and safety rules aligned to current repo workflows.

Evidence Packet

• Commit under test: 5175489
• Runtime environment:
  • OS: Darwin 25.3.0 arm64
  • Python 3.14.0
  • go version go1.25.7 darwin/arm64
  • Node: v22.19.0
• Minimal repro:
  1. Follow the repo's current local validation/CI-triage path.
  2. Observe the behavior described above for this issue.
• Expected behavior: deterministic, documented behavior matching acceptance criteria below.
• Actual behavior: behavior can be inconsistent for the scenario described above.

Acceptance Criteria

• Implement the smallest code change that addresses the proven pain point.
• Add focused regression test coverage for the changed behavior.
• Ensure backward compatibility expectations are explicit in tests/docs.