Add an offline skill quickstart smoke test

[kriptoburak]

Goal

Protect the README's first TweetClaw workflow with an offline regression test.

Scope

• Load the public plugin through its normal entry point.
• Reuse the request stubs in tests/request.test.ts.
• Exercise one documented read-only tweet workflow.
• Assert request mapping and returned fixture data.
• Never contact a remote service or read credentials.

Acceptance Criteria

• The test uses deterministic local fixtures.
• The test fails when documented request mapping changes.
• The repository's full test command passes.
• Keep command names and public response shapes unchanged.
• Update documentation only when the tested example needs correction.

Starting Points

• README
• Request tests
• Plugin tests

This task should fit within 1 working day. It supports newcomer onboarding and OpenSSF evidence.