Add comparison document for StructuredParams and similar gems

[Syati]

No description provided.

[Copilot]

Pull Request Overview

This PR adds comprehensive documentation comparing StructuredParams with other parameter handling gems in the Ruby/Rails ecosystem. The comparison provides detailed feature matrices, code examples, and migration guidance to help developers choose the right tool for their needs.

• Adds a new comparison document with feature matrices for StructuredParams vs typed_params, dry-validation, and reform
• Provides detailed code examples showing the differences between each gem's approach
• Includes migration guides with before/after code examples for transitioning from other gems
• Updates README files to reference the new comparison documentation

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
docs/comparison.md	New comprehensive comparison document with feature matrices, code examples, and migration guides
README.md	Adds link to new gem comparison documentation
README_ja.md	Adds link to new gem comparison documentation and fixes minor typos

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[Copilot]

The katakana spelling 'イニシャライザ' should be 'イニシャライザー' (with ー) to be more accurate for 'initializer'.

Suggested change

	# 2. イニシャライザで型を登録
	# 2. イニシャライザーで型を登録

[Copilot]

Missing space between 'ActiveModel' and 'バリデーション' for better readability.

Suggested change

	- **[バリデーション](docs/validation.md)** - ネスト構造でのActiveModelバリデーション使用
	- **[バリデーション](docs/validation.md)** - ネスト構造での ActiveModel バリデーション使用

[Copilot]

Missing space between '自動' and 'permit' for consistency with other entries.

Suggested change

	- **[Strong Parameters](docs/strong-parameters.md)** - 自動permit リスト生成
	- **[Strong Parameters](docs/strong-parameters.md)** - 自動 permit リスト生成