:bug: git_issue_agent hard codes host and port

[esnible]

Describe the bug

The git_issue_agent hard codes the host and port (overriding the HOST and PORT env vars).

This makes it a poor example, as Kagenti supplies these things, but it ignores them.
There may be security implications when testing -- it is difficult to force the agent to listen only on localhost.

Steps To Reproduce

As part of local development, do HOST=localhost PORT=8001 uv run --no-sync server --host localhost --port 8002 and observe the agent self-reports that it is listening on 0.0.0.0:8000.

Expected Behavior

The agent should respond to $HOST and $PORT variables, or perhaps --host and --port command-line arguments.

Additional Context

No response

[esnible]

Also the generic_agent.

[esnible]

Note that the code's config.py expects the port to arrive in SERVICE_PORT env var, but Kagenti sets the PORT env var.