Add explicit aiohttp>=3.13.4 dependency constraint to pyproject.toml to
remediate CVE-2026-34515, a high-severity open redirect vulnerability in
aiohttp that affects the A2A server HTTP transport, MCP tool source
fetching, and agent communication layers.
The uv.lock already resolves aiohttp to 3.13.5 which satisfies the
>=3.13.4 constraint. Adding the explicit constraint ensures vulnerable
versions (<3.13.4) cannot be installed even if upstream transitive
dependency constraints are loosened.
ISSUES CLOSED: #1544