ci: Extract docs versioning and release into reusable workflows

[vdusek]

Summary

Docs versioning (manual_version_docs.yaml):

• Extract the inline version_docs job from manual_release_stable.yaml into a standalone reusable workflow
• Can be triggered manually from the GitHub UI (with an optional ref input) or called from the release pipeline
• Fix api:version ENOENT bug by running docusaurus commands through uv run
• Clean up all existing versions for the same major version, not just exact major.minor match
• Remove non-docs artifacts (pyproject.toml, .gitignore, caches) from versioned doc snapshots
• Align doc_release ref to use version_docs_commitish instead of default_branch

Docs release (manual_release_docs.yaml):

• Rename _release_docs.yaml to manual_release_docs.yaml to match the naming convention
• Add optional ref input to workflow_dispatch so it can be triggered from the GitHub UI with a specific ref (falling back to the default branch)
• Replace CHECKOUT_REF env var approach with a Determine checkout ref step, consistent with manual_version_docs.yaml
• Update all references in manual_release_stable.yaml and on_master.yaml

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.42%. Comparing base (6ae308d) to head (aff224f).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #728      +/-   ##
==========================================
+ Coverage   95.28%   95.42%   +0.13%     
==========================================
  Files          45       45              
  Lines        5114     5114              
==========================================
+ Hits         4873     4880       +7     
+ Misses        241      234       -7     

Flag	Coverage Δ
integration	95.42% <ø> (+0.13%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.