東北キャラクター追加とデフォルト変更 (#13)

refactor: Remove unnecessary comment about GPU version in Dockerfile

fix: Update Dockerfile to streamline voicevox core download and Python package installation

Refactor Dockerfile: remove unnecessary logs directory creation

Add error handling to Dockerfile download command for build stability

Fix Dockerfile to use correct target for downloading voicevox core

Add Dockerfile to set up application environment and dependencies