feat: complete Wallonia land cover and terrain sources

backend/README.md

@@ -1603,12 +1603,12 @@ stored as `bounded_selection`.
 
 The Wallonia map flow uses bounded PICC vector products, the queryable legal
 SPW flood-hazard polygon layer and provisioned official WALOUS land-cover
-rasters. Provision the 2020 and 2023 source editions once in the persistent
+rasters. Provision the 2018, 2020 and 2023 source editions once in the persistent
 storage mount:
 
 ```bash
 docker exec geointel python /app/scripts/provision_walous_sources.py \
-  --years 2020 2023 \
+  --years 2018 2020 2023 \
   --destination /app/storage/source-cache/walous
 ```
 
@@ -1616,12 +1616,14 @@ The provisioner verifies advertised archive sizes, safe ZIP structure,
 EPSG:3812, one band, 1 m cells, the official non-contiguous class codes
 `1,2,3,4,5,6,7,8,9,80,90` and SHA-256 checksums. It does not run at
 application startup. `GET .../datasets/walous/products` therefore reports
-`source_not_provisioned` until both source files exist.
+`source_not_provisioned` for each edition whose source file is absent.
 
 For a bounded Walloon selection the browser persists the latest edition and
 all other configured comparable editions. `POST .../raster/walous/select`
 returns cell-area hectares; the temporal API compares the same semantic metric
-keys for 2020 and 2023. WALOUS is land cover, not legal land use, ownership,
+keys for 2018, 2020 and 2023. The 2018 stacked classes use the official visible-
+class crosswalk and retain the earlier-method limitation. WALOUS is land cover,
+not legal land use, ownership,
 tree count, timber volume or water volume.
 
 The class semantics follow the official raster codes, not display-list
@@ -1636,10 +1638,13 @@ Settings: `WALOUS_ENABLED`, `WALOUS_SOURCE_DIR`,
 `WALOUS_MAX_PIXELS`. The SPW flood polygon adapter uses
 `SPW_FLOOD_HAZARD_ENABLED` and `SPW_FLOOD_HAZARD_MAPSERVER_URL`.
 
-The official Walloon 2021-2022 DTM is currently not an implicit runtime asset:
-the published 1 m whole-region artifact is about 41 GB and the 0.5 m INSPIRE
-artifact about 213 GB. A later operator capacity plan must define storage,
-partitioning and refresh before it can be called operational.
+The official Walloon 2021-2022 1 m MNT is an explicit operator asset. Provision
+it once with `scripts/provision_spw_terrain_source.py`; the runtime then reads
+only bounded windows and persists 5 m analysis derivatives. The full 0.5 m
+artifact remains intentionally excluded because it adds no V1 metric and is
+about 213 GB. Settings: `SPW_TERRAIN_ENABLED`, `SPW_TERRAIN_SOURCE_DIR`,
+`SPW_TERRAIN_ANALYSIS_RESOLUTION_M`, `SPW_TERRAIN_MAX_SIDE_M` and
+`SPW_TERRAIN_MAX_PIXELS`.
 
 Provision the official DOV soil polygons for Mol through the existing vector
 upload path: