Reframe as Agent Workflow Lab

[KyleBrierley]

What changed

• Reframe the repository as Agent Workflow Lab, a reusable collection of AI coding-agent workflow exercises.
• Replace interview-specific language in repository guidance and the configuration exercise.
• Recast the Exercise 08 draft as a timed engineering change and handoff scenario.
• Add a read-only GitHub Actions matrix that runs all three JavaScript fixture suites on pull requests and pushes to main.

Why

The repository should present as a durable engineering artifact rather than interview practice while preserving the same practical exercises and fixtures.

Impact

Documentation and fixture labels now use the new public positioning. No fixture behavior changes. Contributors get automated regression checks for every runnable JavaScript fixture.

Validation

• npm test - legacy widget fixture
• npm test - ticket search fixture
• npm test - changelog helper fixture
• Workflow YAML parse
• git diff --check