Refactor GitHub Actions workflows

Rework CI/CD by replacing and reorganizing GitHub Actions workflows. Added build-ci.yml (typecheck/test + matrix builds), release-downstream.yml (dispatch downstream releases), and release-tag.yml (tag validation + trigger). Renamed pr-build.yml → build-pr.yml and release.yml → release-publish.yml to use input-driven release flows. Removed deprecated workflows (auto-release.yml, build.yml) and deleted locale README files under docs (README_ar/ja/ko/ru/zh-CN/zh-TW). Changes include artifact matrix builds, caching and optimized Windows assembly steps, OpenAPI schema publishing to NapCatDocs, and explicit downstream workflow dispatching on release.