Bump version to 0.3.1

[shobhit-seg]

Summary

• update the macOS About version to 0.3.1
• bump project and lockfile metadata to 0.3.1
• keep the checked-in Homebrew cask version aligned

Validation

• uv lock --check
• uv run ruff check .
• uv run ruff format --check .
• uv run pytest (138 passed)

[abhi204]

🤖 AI pre-review — posted by Claude Code on behalf of @abhi204 (model: claude-haiku-4-5-20251001). Not a formal review; @abhi204 still signs off.

No blocking issues found. Checked for bugs, security, and CLAUDE.md compliance. Version bump is consistent across all four files and validated by test suite and linting.