feat(cli): add the console script pi-agent-cli-lc and document the Zed custom agent - #45

…d custom agent

`uvx <package>` runs the executable that has the name of the package, and it stops with an
error when the package has none (uv 0.7 and later). The package `pi-agent-cli-lc` had only the
script `pi-agent-cli`, so `uvx pi-agent-cli-lc==0.6.0` failed. The ACP registry starts a PyPI
agent only in this form (`uvx <package> <args>`, no `--from`; registry issue 296), so a registry
entry needs a script that has the name of the package.

- pyproject.toml of pi-agent-cli: a second script `pi-agent-cli-lc` with the same entry point.
  `pi-agent-cli` stays.
- test_console_scripts.py: a script with the name of the package exists, the old name stays,
  and the entry point can be imported.
- README: the section "In Zed (custom agent)" with the `agent_servers` entry
  (`uvx --from pi-agent-cli-lc`), the place of the model and key settings, and the entry for a
  checkout. The package README names both uvx forms.
- CHANGELOG [Unreleased]: two entries under "Added".

Checked:
- The new test fails on main (1 failed, 2 passed) and passes with the script (3 passed).
- A wheel built from a copy of the package (version 0.6.1.dev0, outside the workspace):
  `uvx --find-links <dir> pi-agent-cli-lc==0.6.1.dev0 --help` exits 0. The published 0.6.0 in
  the same form exits 1 with "An executable named `pi-agent-cli-lc` is not provided by
  package `pi-agent-cli-lc`."
- `initialize` through that uvx command, with an empty home: the answer comes in 1.6 s;
  `authMethods` is still [] (the registry also needs a login method; not part of this change).
- The command of the README entry ran with the published 0.6.0 (`--from pi-agent-cli-lc --with
  "pi-agent-core-lc[deepseek]" pi-agent-cli`): the agent answered `initialize` and ended when
  stdin closed. It was not run inside Zed.
- Ruff check and format check pass. The temporary directories of the uv runs are removed.