[DEFER] Add lightweight ADR process for governance-impacting decisions

[mark-e-deyoung]

Summary

Introduce a lightweight ADR process for governance-impacting decisions.

Problem

Major governance changes (CI tiering, release controls, contribution enforcement) currently rely on PR discussion only, which can make long-term rationale hard to audit.

Proposal

• Add docs/adr/ with a small ADR template.
• Require ADR for changes to governance/security/release policy boundaries.
• Link ADRs from relevant policy sections.

Acceptance criteria

• ADR template and process are documented.
• At least one recent governance decision is captured as an ADR example.
• Policy docs reference ADR usage triggers.

Category

DEFER