fix(freehire-search): say what --region is, and warn when it matches a thin bucket (#651)

* fix(freehire-search): warn when --region gets a value outside the vocabulary

freehire's contract - the openapi Regions enum and RegionValues in vocab.go -
defines a closed set: nine buckets plus none. Anything else is a stray tag, so a
region filter on us or any other country code matches a handful of postings and
reads as an empty or thin market, which is how #616 started.

search now checks the requested values (--region and the --facet regions= escape
hatch, case-insensitively) against that set and, when one falls outside it, writes
one JSON line on stderr after the results, with code REGION_VALUE_UNKNOWN. The
result count is deliberately not consulted: a broad query returns real hits under a
stray tag and the parameter is still wrong. stdout stays clean JSON, exit code 0.

Tests are unit-level with a stubbed fetch: no extra request to the free API, and no
change to the existing search tests.

* changelog: place the #651 entry under [Unreleased]

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Mads Lorentzen <madslorentzen_17@hotmail.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

.agents/skills/freehire-search/cli/README.md

@@ -43,6 +43,9 @@ Compose (`make up` → API on `:8080`, same `/api/v1/...` paths).
 
 `search` accepts `--format json|table|plain` (default `json`); `detail` accepts `--format json|plain`.
 All errors are written to **stderr** as `{ "error": "...", "code": "..." }` with exit code `1`.
+One diagnostic is a warning instead: a `--region` value outside the documented vocabulary
+prints `{ "warning": "...", "code": "REGION_VALUE_UNKNOWN" }` to stderr after the results,
+and exits `0`, leaving stdout a valid JSON document.
 
 `search` hits the API's agent endpoint, so every JSON result already carries the
 posting's **full** description (Markdown by default, `--description-format