Build and publishing

[alDuncanson]

This pull request updates the project's versioning and release workflow to use the uv tool, removes legacy version management code, and improves project metadata and documentation. The most important changes are grouped below.

Versioning and Release Workflow Updates

• Switched all versioning, tagging, and release commands in the justfile to use uv instead of hatch. This affects the version, bump, tag, and release tasks.
• Updated the GitHub Actions release workflow to verify the project version using uv version --short instead of parsing the version from a Python file.

Project Metadata and Configuration

• Set the project version directly in pyproject.toml and added comprehensive metadata fields (authors, license, keywords, classifiers, URLs). Switched the build backend to uv_build and removed legacy hatch configuration. [1] [2]

Codebase Cleanup

• Removed the _version.py file from both packages/common/src/handler_common/ and src/a2a_handler/, eliminating the old single-source-of-truth for the version string.
• Updated imports in src/a2a_handler/__init__.py and src/a2a_handler/tui.py to retrieve the version dynamically using importlib.metadata.version("a2a-handler"). [1] [2]

Documentation Improvements

• Added new just commands (bump, tag, release) to both AGENTS.md and CONTRIBUTING.md to document the updated development workflow. [1] [2]