feat(fe): impl problem create testcase page

[sONg20NOW]

Description

problem-create의 테스트 케이스 탭 작업을 완료했습니다.

Additional context

피그마 링크

테스트 케이스가 있을 때

테스트 케이스가 없을 때

백엔드 연동 전에 UI 작업만 먼저 완료했습니다.

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closes TAS-2646

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines
• Read the Contributing Guidelines and follow the Commit Convention
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[gemini-code-assist]

Code Review

This pull request replaces the placeholder TestsPage with a functional TestcasePage component for managing problem test cases. The review feedback highlights several issues in the new implementation: the textarea elements for input and output are not currently bound to the component state, preventing user input from being saved. Additionally, the removeAll function incorrectly resets the ID counter to 0 instead of 1, and there are typos in both the Korean UI text and Tailwind CSS class names (itmes-center).

[skkuding-bot]

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