Rename api to openapi (#186)

[kimurash]

• Close OpenAPのディレクトリ名を変更する #186

やったこと

• タイトル参照
• PRのテンプレートを修正した

確認した方法

❯ npm run lint

> lint
> npx @redocly/cli lint openapi.yml

Need to install the following packages:
@redocly/cli@1.34.4
Ok to proceed? (y) y

validating openapi.yml...
openapi.yml: validated in 72ms

Woohoo! Your API description is valid. 🎉

[Copilot]

Pull Request Overview

This pull request renames references from "api" to "openapi" across several configuration, documentation, and workflow files to better reflect the API specification location.

• Updated input targets in orval configuration files
• Updated file paths in documentation and CI/CD workflows
• Revised the pull request template to include a new issue reference header

Reviewed Changes

Copilot reviewed 7 out of 27 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
orval.config.js	Updated target path from './api/bundle.yml' to './openapi/bundle.yml'
orval.config.dev.js	Updated target paths similarly in multiple sections
openapi/README.md	Updated directory name in README from 'api' to 'openapi'
README.dev.md	Updated mock command file path from './api/openapi.yml' to './openapi/openapi.yml'
.github/workflows/validate-spec.yml	Updated lint command file path
.github/workflows/publish-spec.yml	Updated working directory and spec-file references
.github/PULL_REQUEST_TEMPLATE.md	Revised header and comments for better issue reference structure