docs: add comprehensive development guidelines

[Yusuke4869]

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[Copilot]

Pull Request Overview

This PR introduces comprehensive development guidelines to standardize coding practices, architecture design, and documentation across the project. The guidelines establish consistent approaches to TypeScript development with emphasis on type safety, clean architecture principles, and maintainable code practices.

• Establishes foundational development standards covering architecture, coding practices, API design, refactoring, and documentation
• Implements clean architecture principles with clear layer separation and dependency control
• Provides structured checklists for quality assurance across all development domains

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
docs/README.md	Central documentation index with project structure and technology stack overview
docs/architecture.md	Clean architecture principles defining layer separation, dependency rules, and design patterns
docs/coding-standards.md	TypeScript coding standards emphasizing type safety, naming conventions, and function design
docs/api-design.md	RESTful API design principles with consistent response formats and security guidelines
docs/refactoring.md	Systematic refactoring approach focusing on responsibility separation and type safety
docs/documentation.md	Markdown documentation standards with formatting rules and quality checklists

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