Add API for GitManager features

[reddevilmidzy]

Summary

기존에 구현하였던 리비전 기능에 API를 추가하였습니다.

API

• POST /problems/init/{problem_id}: 문제 생성 API
  • (생각해보니까 유저가 문제를 생성하려는 시점에는 problem_id를 알 수가 없군요. auto increment 값으로 변경해야 겠네요.)
• POST /changes/{problem_id}/commit body: {"message": "..."}: 스테이지에 올라온 변경사항을 커밋한다.
  • 성공시 200 리턴 {"commit": ""}
• GET /changes/{problem_id}/log: 커밋 로그를 가져온다.
  • user, time, path, message, paths 포함
  • ex)

[
    {
        "message": "create message",
        "paths": [
            {
                "path": "tests/e.py",
                "status": "ADDED"
            },
            {
                "path": "tests/tmp.py",
                "status": "ADDED"
            }
        ],
        "time": 1760694085,
        "user": "admin"
    },
    {
        "message": "create message",
        "paths": [
            {
                "path": "solutions/c.py",
                "status": "ADDED"
            }
        ],
        "time": 1760693623,
        "user": "admin"
    }
]

• GET /changes/{problem_id}/status: 커밋되지 않은 변경사항(스테이징 영역)을 가져온다.

[
    {
        "status": "ADDED",
        "path": "solutions/e.py"
    }
]

[Copilot]

Pull Request Overview

This PR adds API endpoints for Git-based revision management features to enable version control for problem files. The implementation exposes existing GitManager functionality through REST APIs.

Key Changes:

• Added three new API endpoints for Git operations: problem initialization, commit management, and status tracking
• Refactored GitManager to support stateless operation by accepting problem_id as a parameter
• Updated tests to reflect API path changes from singular (/solution) to plural (/solutions)

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/lib.rs	Added new router configurations for /problems/init and /changes endpoints with GitManager state
src/file_manager/handlers.rs	Implemented handler functions for create_problem, commit_changes, get_log, and get_status endpoints
src/file_manager/git.rs	Refactored GitManager from stateful (storing problem_id) to stateless design, made structs/methods public, added Serialize traits
src/file_manager/models.rs	Added CommitRequest model for commit message payload
src/file_manager/mod.rs	Exposed git module contents via pub(crate) use
tests/file_manager/handlers.rs	Updated all test cases to use new API paths and added integration tests for new Git endpoints

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}