docs: close Governed Cognition milestone

[eamirian]

Problem and scope

Reconcile the completed 0.4.x Governed Cognition milestone after the public ACE Core 0.4.4 and independent Market Intelligence external-consumer journey passed. This change owns the public roadmap, evidence archive, one immutable closeout receipt, and their contract tests. It does not change runtime code, authority, APIs, or historical evidence records.

Closes #3.

Product boundary and compatibility

• GC1 advances from active to passed.
• 0.5.0 remains next under its own T1 and B1 gates.
• The claim remains bounded to the documented single-node topology and trusted in-process extensions.
• No public contract, migration, MCP tool, model authority, or domain-specific Core behavior changes.

Evidence

• 48 focused cognition, restart, CLI, roadmap, and evidence tests passed.
• 10 packaging identity tests passed.
• Ruff lint and format checks passed.
• Independent Market PR #3 CI passed; archived runtime receipt SHA-256: b239b314b34c3dfedddb72907b63abe5bf3197013b8d1460466ff4942f714682.
• Public Core 0.4.4 trusted publication and release gates passed.

Risk and rollback

Documentation-only reconciliation. Revert this commit if any receipt identity or acceptance interpretation is falsified; immutable historical 0.4.1/0.4.2 records remain unchanged.

Checklist

• I used no private data, credentials, proprietary fixtures, or private-extension code.
• I updated documentation for changed public behavior and did not overstate maturity.
• I ran focused checks, relevant conformance checks, Ruff for changed Python, and git diff --check.
• If roadmap-related, I linked or updated the public issue/Project item.
• Security-sensitive details were reported privately under SECURITY.md (not applicable; none included).