Change license from MIT to GPLv2+

[mkusaka]

Summary

• Replace MIT license with GPLv2+ to comply with the iterm2 Python package dependency, which is licensed under GPLv2+
• Update LICENSE file with full GPLv2 text and copyright notice ("or later" clause included)
• Update pyproject.toml classifier to GNU General Public License v2 or later (GPLv2+)
• Update README.md license reference from MIT to GPLv2+

Why

The project depends on the iterm2 package (GPLv2+) as a runtime dependency, importing it directly throughout the codebase. Distributing under MIT is incompatible with the copyleft requirements of the GPL. Relicensing to GPLv2+ is the simplest way to resolve this.

Test plan

• Verify LICENSE file contains the standard GPLv2 text with the project copyright notice
• Verify pyproject.toml classifier reflects GPLv2+
• Verify README.md references GPLv2+ instead of MIT
• Verify no remaining MIT references in the repository (other than unrelated files)