Add governed Statbel edition probe

docs/ENVIRONMENT_SPEC.md

@@ -29,6 +29,8 @@ GRB_WFS_URL=
 # Explicit read-only source-edition probes (no provider import).
 SOURCE_CATALOG_PROBE_ENABLED=true
 SOURCE_CATALOG_GRB_WFS_URL=https://geo.api.vlaanderen.be/GRB/wfs
+SOURCE_CATALOG_STATBEL_DCAT_URL=https://doc.statbel.be/publications/DCAT/DCAT_opendata_datasets.ttl
+SOURCE_CATALOG_STATBEL_MAX_RESPONSE_MB=5
 SOURCE_CATALOG_ALZ_RELEASE_URL=https://landbouwcijfers.vlaanderen.be/open-geodata-landbouwgebruikspercelen
 SOURCE_CATALOG_PROBE_TIMEOUT_SECONDS=10
 SOURCE_CATALOG_PROBE_MAX_RESPONSE_MB=2
@@ -36,6 +38,11 @@ SOURCE_CATALOG_PROBE_CACHE_TTL_SECONDS=900
 OSM_OVERPASS_URL=https://overpass-api.de/api/interpreter
 ```
 
+The Statbel limit is separate because the official Turtle catalog is larger
+than the bounded OGC/HTML metadata responses. The probe parses only release
+metadata and validates distribution identities; it never follows population
+ZIP or XLSX links.
+
 ### Frontend
 
 ```env