Add PR helper scripts

[TamaruNorio]

Summary

• Added git_preflight.ps1 for PR前の状態確認。
• Added pr_body.ps1 for PR本文テンプレート生成。
• Added reusable PR body template.
• Documented helper script usage in README.

Test

• .\scripts\dev_check.ps1
• pytest completed
• blocked text scan completed
• logs/real_device/ ignore check completed

Safety

• No real device communication
• real_device_check.py not executed
• logs/real_device/ is excluded from Git
• git push executed manually
• PR creation and merge are manual

Notes

• This change only adds helper scripts and documentation for PR preparation.