[examples]: Add a listnamespace example

[Vaughan-Temporal]

Stacked on #154. Docs and config only — no Go.

A runnable example for calling WorkflowService.ListNamespaces against Temporal Cloud through the proxy, driven by
curl rather than a worker so the behaviour can be checked without an SDK.

The point the README makes: nothing in config.yaml asks for translation. The upstream's .tmprl.cloud address is
what turns it on. That is the design from #154 working as intended, and it is worth seeing what the resulting config
does not contain.

Walks through:

• ListNamespaces succeeding via the proxy
• the same call sent straight at Cloud, failing with namespace mismatch between header "quickstart" and request body ""
• paging via nextPageToken
• GetSystemInfo and DescribeNamespace still reaching the frontend untouched
• an optional namespaces.rules block for short namespace names

Scope

+248 / −0, 3 files. Verified the config loads, validates, and the proxy starts on it.

---

Stack

	PR
1	#152	translation library — mechanism only
2	#153	ListNamespaces → CloudService.GetNamespaces mapping
3	#154	integration — first behaviour change
4	#155	listnamespace example

Merge bottom-up. Each PR targets the one above it, so its diff shows only its own change.

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