Describe the read model argument as an identifier

[woksin]

Summary

read-models get, snapshots and instances send their positional argument as the read model identifier, but the help text called it a container name and pointed at cratis read-models list — which prints both an Identifier and a Container column.

A user following the help picked the wrong column and the server answered with an unhandled error rather than a useful message.

No tracking issue exists; found capturing CLI output with 3.1.6 against Chronicle 18.1.6.

Fixed

• The <READ_MODEL> argument is described as the read model identifier and names the column to read it from, matching what the commands actually send.

Notes for review

• No behaviour change: the wire value was always ReadModelIdentifier. This aligns the [Description], the [LlmOption] metadata and the settings doc comment with it.
• The server side of the same mistake is fixed separately in Cratis/Chronicle fix/read-model-lookup-miss-guard, which turns the resulting NullReferenceException into a meaningful error. The two are independent; either can merge first.
• GetReadModelInstancesCommand catches an RPC error whose detail contains "NullReferenceException" and reports it as "read model is client-owned". That was papering over the server defect above and is the wrong explanation for an unknown identifier — worth re-scoping once the Chronicle fix ships. Left untouched here.
• read-models occurrences uses a different argument name (<READ_MODEL_TYPE>) and may be worth a consistency pass.

Verification

• New spec asserts the description says identifier, does not say container name, and names the Identifier column that ListReadModelsCommand prints — so help text and wire payload cannot drift apart again.
• Cli.Specs: 1,111 tests passing.