docs(agents): note the control-plane copy of charts/api7

[jarvis9443]

api7/api7ee-3-control-plane carries a copy of charts/api7 at helm/, packaged as api7ee3-dev.tgz and installed by CP's e2e workflow. Nothing links or checks the two, so a change made here silently leaves the copy behind — #333 did exactly that, and the copy needed a follow-up PR.

Records the relationship next to the existing source-of-truth notes for aisix-cp and ngxdig. Docs only, no chart change, so no version bump.

Summary by CodeRabbit

• Documentation
  • Added guidance for the charts/api7 downstream copy, including artifact usage, end-to-end testing, source-of-truth status, and synchronization requirements.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 86911d88-702b-4e0d-9c2d-1040da3ce8cc

📥 Commits

Reviewing files that changed from the base of the PR and between 558a18b and 50c6b17.

📒 Files selected for processing (1)

• AGENTS.md

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📝 Walkthrough

Walkthrough

Changes

Downstream chart documentation

Layer / File(s)	Summary
Document downstream chart copy AGENTS.md	Documents the charts/api7 downstream copy, its api7ee3-dev.tgz package, e2e usage, source-of-truth status, and manual synchronization requirement.

Estimated code review effort: 1 (Trivial) | ~2 minutes

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the documentation change for the control-plane copy of charts/api7.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
E2e Test Quality Review	✅ Passed	PASS: HEAD changes only AGENTS.md documentation; no E2E test or production logic is in scope, and the note directly documents the downstream chart sync risk.
Security Check	✅ Passed	The patch changes only two documentation lines in AGENTS.md; it adds no code, configuration, endpoints, logging, persistence, TLS, authorization, isolation, or secret-resolution behavior.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/agents-cp-chart-copy

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