chore: bump version to 0.0.15

[wardmos]

Summary

• document the release branch naming convention
• bump the package version from 0.0.14 to 0.0.15

Checks

• .venv/bin/ruff check src tests
• .venv/bin/ruff format --check src tests
• QT_QPA_PLATFORM=offscreen .venv/bin/pytest -q (1424 passed, 3 skipped)
• built the 0.0.15 sdist and wheel
• twine check passed for both distributions

Notes

• Merge the remaining PyObjC 12.2.1 updates (build(deps): bump pyobjc-framework-quartz from 12.2 to 12.2.1 #121, build(deps): bump pyobjc-framework-screencapturekit from 12.2 to 12.2.1 #84, then build(deps): bump pyobjc-framework-vision from 12.2 to 12.2.1 #87 after Quartz) before tagging v0.0.15.
• This PR does not create or push the release tag.