Extract GitHub Projects operations from the command engine

[codeforester]

Context

cli/python/base_github_projects/engine.py is smaller after recent helper extraction, but it still mixes CLI command dispatch with GraphQL project operations. It also passes sys.modules[__name__] as an operations object for command helpers, which keeps implementation seams implicit.

Scope

• Extract a GitHub Project operations/client layer used by command helpers.
• Replace implicit module-as-ops coupling with an explicit operations object or protocol.
• Preserve existing basectl gh project behavior.

Validation

• Focused GitHub Projects command tests with fake operations.
• Existing base_github_projects tests.
• git diff --check.