Add official source edition probes

docs/API_CONTRACTS.md

@@ -412,6 +412,26 @@ Dataset or silently refreshes a publication. Fixed editions and scenarios are
 not marked stale merely because their source date is old. Unknown sources are
 `review_required` until an explicit publication policy is defined.
 
+### GET `/api/v1/projects/{project_id}/datasets/source-catalog-probes`
+
+Performs an explicit, read-only release probe for the allowlisted GRB WFS and
+most-recent orthophoto WMS. The endpoint reads bounded `GetCapabilities`
+responses, confirms the expected layers and follows only HTTPS ISO 19139
+`GetRecordById` links on `metadata.vlaanderen.be`. Query parameter
+`refresh=true` bypasses the short in-memory response cache.
+
+Each provider item returns service reachability, matched/missing layers, the
+official metadata identifier, title, edition, publication/metadata dates,
+local `source_version` and one comparison status: `same`, `different`,
+`not_comparable`, `no_local_data` or `unavailable`. Provider status is
+`available`, `degraded`, `unavailable` or `disabled`. A difference means only
+that an operator should review provenance; it is not an update instruction.
+
+The endpoint accepts no arbitrary URL, feature query, area or layer. It does
+not fetch vector features, raster pixels or models, create jobs/datasets, write
+to PostGIS or trigger an import. The normal `source-freshness` endpoint remains
+local-only and never invokes this probe implicitly.
+
 ### GET `/api/v1/projects/{project_id}/datasets/{dataset_id}`
 
 Return metadata.