ADK Go sample creator

An example earns its place by teaching one thing faster than the package docs can. It must run. Two families set the standard, and which one you are writing decides several of the choices below:

• Engine samples — examples/workflow/*. They exercise ADK itself, need nothing beyond the binary and sometimes a model, and their subject is the shape of a graph.
• Integration samples — examples/agentregistry/*. They talk to a live external service, so they carry cloud prerequisites, credentials, failures worth unwrapping, and output that depends on the reader's own project.

Copy the shape of the nearer family rather than inventing one.

examples/README.md documents an older launcher API (ParseAndRun, FormatSyntax). Follow the templates here, not that file.

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