ci: standardize workflows and chart patterns to match org playbook

[devin-ai-integration]

Summary

Aligns conversion-guide CI/CD workflows and documentation with the qcon-api reference implementation:

• AGENTS.md: Restructured to match qcon-api format — added Architecture, Development Workflow sections; expanded CI/CD section with details about FORCE_JAVASCRIPT_ACTIONS_TO_NODE24, OCI image/chart registry paths, and release-please annotations; updated Project Structure to use /path — description format with /.github/workflows/ entry
• release-retag.yaml: Quoted all $GITHUB_OUTPUT references for shell safety; renamed TAGS → TAG_ARGS variable to match qcon-api convention

All other standardization items (checkout@v6, FORCE_JAVASCRIPT_ACTIONS_TO_NODE24, helm push error guard, tolerant digest parse, yq chart name extraction, shell-safe GHA env blocks, digest guard on sign steps, Chart.yaml annotations, release-please-config.json, affinity conditional) were already applied in a prior PR.

Review & Testing Checklist for Human

• Verify AGENTS.md Architecture section accurately describes the conversion-guide app (nginx-unprivileged on 8080, Gulp build pipeline, Plausible analytics)
• Confirm release-retag.yaml TAG_ARGS rename doesn't conflict with any external references

Notes

Helm lint and kubeconform validation both pass locally. No functional workflow changes — only documentation and shell quoting improvements.

Link to Devin session: https://app.devin.ai/sessions/b477b6dc23784c18940aeae81802106c
Requested by: @kphunter

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✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.