Document validation script entrypoints

[cbusillo]

Summary

• Add a README validation command map for the existing script entrypoints.
• Make the locally documented commands match the workflow metadata and CI usage after the script-reference audit.

Refs #23

Validation

• git diff --check
• actionlint .github/workflows/*.yml
• jq empty .github/github-repo-workflow.json

Notes

• Documentation only; no image behavior changes.

[cbusillo]

Build And Publish Images failed in the runtime-devtools verification build, unrelated to this README-only change.

Evidence from the failed job and failed-job rerun:

• runtime verification passed, including smoke, DB init, downstream helper checks, and Trivy scan.
• CodeQL passed.
• runtime-devtools failed during Docker build while running apt-get update against the xtradeb Chromium PPA.
• Both initial and rerun logs show: Could not connect to ppa.launchpadcontent.net:443 (185.125.190.80), connection timed out followed by Failed to fetch https://ppa.launchpadcontent.net/xtradeb/apps/ubuntu/dists/noble/InRelease.

Run: https://github.com/cbusillo/odoo-docker/actions/runs/25292312296

Leaving this PR open because the build check is red, but the failure appears to be external PPA/network availability rather than a docs regression.