Add Codex repository guidance and validation

CHANGELOG.md

@@ -4,6 +4,17 @@
 
 ### Added
 
+- Repository-level Codex guidance:
+  - `AGENTS.md`
+  - `docs/codex/README.md`
+  - `docs/codex/review-checklist.md`
+  - `docs/codex/task-template.md`
+  - `docs/codex/plans-template.md`
+- Lightweight validation helpers:
+  - `scripts/validate-repo.sh`
+  - `scripts/check-bash.sh`
+  - `scripts/check-ansible.sh`
+  - `scripts/check-docs.sh`
 - Cross-repository operational documentation structure:
   - `infra-run/docs/operations-cheatsheet.md`
   - `platform-projects/docs/platform-cheatsheet.md`
@@ -19,6 +30,7 @@
 
 ### Changed
 
+- Updated root, `infra-run`, Bash, Ansible, platform, and lab README guidance for safety-first usage, validation, and future Codex-driven work.
 - Updated repository and `infra-run` README files to surface the new documentation structure and operational cheatsheets.
 - Updated repository, `infra-run`, and Ansible README files to describe the new hardening automation instead of placeholder-only Ansible structure.