Declare base-cli 0.4.1 as an explicit project dependency

[codeforester]

Goal

Declare base-cli 0.4.1 explicitly in base-demo's project metadata so the
reference Python CLI is independently reproducible.

Background

lib/python/base_demo_cli imports base_cli, but pyproject.toml currently
declares only click and PyYAML. The dependency is supplied indirectly by
the Base runtime and CI PYTHONPATH, and uv.lock has no base-cli entry.

Scope

Update the project dependency metadata and lockfile, then validate the existing
Python CLI without changing its command behavior.

Acceptance Criteria

• pyproject.toml declares base-cli==0.4.1.
• uv.lock records the direct dependency and its resolved transitive graph.
• The base-demo Python CLI tests pass using the declared dependency.
• The repository validation command passes.
• The PR links this issue with Fixes #205.

Validation

• ./tests/validate.sh
• base-demo Python CLI unit tests
• uv lock --check or equivalent lock validation
• git diff --check

Non-Goals

• No changes to the base-cli framework itself.
• No changes to Base's runtime implementation; that is tracked in
  Align Base with base-cli 0.4.1 base#1896.

Project Fields

• Priority: P1
• Area: Python
• Initiative: Adoption Polish
• Size: S

Agent Assignment

• Assignee: @codeforester
• Related upstream alignment issue: Align Base with base-cli 0.4.1 base#1896
• Related release: https://github.com/basefoundry/base-cli/releases/tag/v0.4.1