Refresh AGENTS guidance after Phase 6

[StatPan]

Goal

Keep AGENTS.md as the concise project entry point while preserving older operational context elsewhere.

Derived from #14 Phase 6 dirty branch handoff.

Scope

• Replace or retain the concise AGENTS.md content after reviewing the current dirty diff.
• Confirm legacy operational material remains discoverable in CLAUDE.md or docs.
• Keep this as a documentation/handoff change only.

Out of Scope

• Do not modify runtime code.
• Do not delete historical context unless an alternate reference remains clear.
• Do not combine with approval/SSE, security, or port config changes.

Acceptance Criteria

Functional:

• AGENTS.md accurately points to current execution source, spec source, and next action.
• Historical implementation details are not lost without an alternate reference.
• The file stays short enough to work as a project entry point.

Code/product quality:

• Documentation is current with Phase 6 and next milestone state.
• It follows the workspace-level AGENTS contract.

Verification

• Documentation review.
• git diff --check.

Expected Delivery

• Delivery mode: docs-only PR.
• Review mode: control plane verifies it does not remove useful historical pointers.
• Merge mode: safe to merge without owner escalation unless it changes project operating rules.