Refactor: Define state of selected category out of CategorySelect

[nick-y-ito]

Overview

Please see the issue this PR is based on: #175

Note

• This is a temporary alteration, and this part will be modified again shortly in one of the following PRs.
  • https://github.com/genesis-tech-tribe/nishiki-frontend/pull/165
  • https://github.com/genesis-tech-tribe/nishiki-frontend/pull/167
• I will merge this PR once only one review approves it.

Assignee Checklist:

• [x] The naming convention of the PR title is correct (See the comment at the top of this template)
• [x] The base branch is correct (See: Types of Branches)
• [x] The branch name follows the Branch Naming Conventions
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• [x] The coding style follows the Coding Style Guide
• [x] All the related issues are associated with this PR
• [x] All criteria in the associated issues are met (please tick the checkboxes)
• [x] My changes do not generate new warnings or errors (especially in the console)

Reviewer Checklist:

• [ ] Double-check the "Assignee Checklist"
• [ ] The code follows the generic best practices and our Coding Style Guide
• [ ] The code is well-commented and easy to understand
• [ ] The UI changes accurately reflect the provided design

[nick-y-ito]

@kanta1207 Thank you for your prompt review :)