Automate versioned docs publishing to PyThaiNLP/docs on release

[Copilot]

Documentation for each release was manually copied to PyThaiNLP/docs and the version index had to be hand-updated.

What do these changes do

• Adds .github/workflows/publish-versioned-docs.yml: triggered on release: published, copies PyThaiNLP/dev-docs → PyThaiNLP/docs/{version}/ and updates both index pages
• Adds build_tools/github/update_docs_index.py: helper script with two modes:
  • --docs-dir: regenerates docs/index.html as a landing page listing all version directories, sorted newest-first
  • --dev-docs-index: injects/updates a <!-- BEGIN VERSIONS -->…<!-- END VERSIONS --> block in dev-docs/index.html; idempotent (no-ops if version already present, appends before </body> if markers are absent)

What was wrong

No automation existed to archive dev docs as a versioned snapshot or maintain the version listing when a release was published.

How this fixes it

On each GitHub release the workflow:

1. Strips the v prefix from the tag (v5.3.1 → 5.3.1)
2. Syncs dev-docs/ into docs/{version}/ via rsync
3. Regenerates docs/index.html from the directory listing
4. Prepends the new version entry to dev-docs/index.html
5. Commits and pushes both external repos via PERSONAL_TOKEN

The workflow runs only on PyThaiNLP/pythainlp (not forks) and uses permissions: contents: read for the GITHUB_TOKEN.

Your checklist for this pull request

• Passed code styles and structures
• Passed code linting checks and unit test

Original prompt

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This section details on the original issue you should resolve

<issue_title>Automatic build document to PyThaiNLP/docs when released new version</issue_title>
<issue_description>Now, PyThaiNLP/docs is still want update document by hand when we released new version. I think if github action can automation this step, it will be automation.

Step:

1. Copy PyThaiNLP/dev_docs to PyThaiNLP/docs and name directory as version (without v).
2. Update index.html in PyThaiNLP/dev_docs: Move old version and add new version.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Automatic build document to PyThaiNLP/docs when released new version #1324

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[sonarqubecloud]

Quality Gate failed

Failed conditions
E Security Rating on New Code (required ≥ A)

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[coveralls]

coverage: 66.312%. remained the same
when pulling 57e564c on copilot/automate-docs-build-process
into fcb9210 on dev.