Add package.json with development tooling

[Copilot]

Establishes npm-based dependency management and standardized development commands for the project.

Scripts

• serve - Local development server (live-server:8080)
• lint - JavaScript (ESLint) + HTML (HTMLHint)
• format / format:check - Prettier formatting

Dependencies

• eslint (8.57.0) + eslint-config-prettier - JavaScript linting
• prettier (3.2.5) - Code formatting
• htmlhint (1.1.4) - HTML validation
• live-server (1.2.2) - Development server

Configuration

• Node ≥18.0.0, npm ≥9.0.0
• MIT license
• Project described as Chart.js visualization dashboard

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[最優先] package.json の作成</issue_title>
<issue_description>## 概要
依存関係とnpmスクリプトを管理する package.json を作成する。

背景

• 全てのレビュアー（DevOps/Frontend/PM）が必須として指摘
• 開発コマンドの統一化（lint, format, serve等）
• 依存関係の明示的管理

含めるべき内容

• プロジェクト名・説明・バージョン
• npm scripts（lint, format, serve）
• devDependencies（eslint, prettier, live-server等）

優先度

🔴 最優先（全員一致）</issue_description>

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

• Fixes [最優先] package.json の作成 #4

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.