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/SKILL.md

@@ -169,6 +169,11 @@ result carries at least `id` (the freehire slug), `title`, `company`, `location`
 omit the description — it would swamp a scannable list. All errors are written to
 **stderr** as `{ "error": "...", "code": "..." }` and the process exits with code `1`.
 
+One diagnostic is not an error: a `--region` (or `--facet regions=`) value outside the
+documented vocabulary - `us` is a country code, not a region - prints
+`{ "warning": "...", "code": "REGION_VALUE_UNKNOWN" }` on **stderr** after the results,
+and the process still exits `0` with stdout a valid JSON document.
+
 ## Partial data
 
 Facets are derived per-posting and can be **incomplete** — geography especially.