chore: adds pre-commit (#7242)

### What problem does this PR solve?

Sometimes after we commit the code and open the PR the CI pipeline fails
in Ruff checks. Including a pre-commit we can identify this problem
early and avoid time loss.

### Type of change

- [ ] Bug Fix (non-breaking change which fixes an issue)
- [X] New Feature (non-breaking change which adds functionality)
- [ ] Documentation Update
- [ ] Refactoring
- [ ] Performance Improvement
- [ ] Other (please describe):

README_ja.md

@@ -258,7 +258,7 @@ docker build --platform linux/amd64 -f Dockerfile -t infiniflow/ragflow:nightly
 1. uv をインストールする。すでにインストールされている場合は、このステップをスキップしてください:
 
    ```bash
-   pipx install uv
+   pipx install uv pre-commit
    ```
 
 2. ソースコードをクローンし、Python の依存関係をインストールする:
@@ -267,6 +267,7 @@ docker build --platform linux/amd64 -f Dockerfile -t infiniflow/ragflow:nightly
    git clone https://github.com/infiniflow/ragflow.git
    cd ragflow/
    uv sync --python 3.10 --all-extras # install RAGFlow dependent python modules
+   pre-commit install
    ```
 
 3. Docker Compose を使用して依存サービス（MinIO、Elasticsearch、Redis、MySQL）を起動する: