docs: link organization lessons learned controls

[Elodie Mirza (elodiejmirza)]

BLUF

• Adds a lightweight link from this repo's guidance to the central SoloSentryOrg lessons learned register.
• Keeps the change deliberately small and aligned with the repo's existing contributor guidance.

Changes

• Updates AGENTS.md with central register review expectations for org-spanning work.
• Requires complexity removed or justified for cross-repo changes.
• Requires repeated same-cluster failures to stop for RCA/register update.

Security Review Evidence

• Documentation-only change reviewed for policy weakening, secret exposure, and governance-control drift.
• No runtime, dependency, workflow permission, secret handling, or build behavior changed.
• No secrets, tokens, credentials, private keys, or private configuration were added.

Verification

• git diff --check
• Diff secret-pattern review across all rollout repos: no matches.
• Live GHAS baseline check confirmed active repos report enforced:248696 during rollout verification.

Project Update

• No GitHub Project update was applied; this is a repo-local guidance link to the central governance register.