Add API docs reliability checks

[weilun88313]

Summary

• sync the public backup OpenAPI artifact with the v0.23.1 source so all three published copies are identical
• make the public asset generator understand Mintlify OpenAPI navigation entries and cover all 41 navigation pages, including all 28 API operations
• add 27 permanent redirects from legacy API reference routes to the current Mintlify-generated routes
• add deterministic tests and a Docs Quality workflow for generated assets, JSON/OpenAPI consistency, legacy key guidance, and OpenAPI linting

Validation

• python3 -m unittest scripts/test_sync_public_assets.py
• python3 scripts/sync-public-assets.py --check
• jq empty docs.json api-catalog.json openapi.json api-reference/openapi.json api-reference-backup/openapi.json
• confirmed all three OpenAPI artifacts are byte-identical
• npx --yes @redocly/cli@2.39.0 lint openapi.json

Redocly validates the specification successfully. It reports 13 existing non-blocking warnings for the missing license/tag descriptions and unused response components.