Add a2a-sdk>=0.3.0 to [project.dependencies] in pyproject.toml.
The specification mandates that both local (stdio) and server (HTTP)
transports use the A2A Python SDK (ADR-047). Previously the package
was absent from pyproject.toml and uv.lock, making the project
non-compliant with the spec requirement.
Changes:
- Add 'a2a-sdk>=0.3.0' to [project.dependencies] in pyproject.toml
- Regenerate uv.lock to include a2a-sdk 0.3.25 and its transitive deps
- Add Behave scenarios confirming a2a is importable as a project dependency
- Add step definitions for the new TDD scenarios
ISSUES CLOSED: #2922
