feat: add governed hydrology and historical imagery

docs/DATA_SOURCES.md

@@ -214,9 +214,6 @@ These sources are available from their public authorities but are not silently
 treated as loaded GeoIntel data. The Source inventory labels them separately
 until a governed operator import, provenance record and validation pass exist.
 
-- Historical orthophotos (Digitaal Vlaanderen): 1971 and 1979-1990 through
-  the `OKZ` WMS, with additional dated mosaics as separate products. Suitable
-  for visual/image evolution after a bounded acquisition contract is added.
 - Biologische Waarderingskaart / Natura 2000 (INBO), state 2025: suitable for
   habitat, biotope and ecological-value analysis, not a continuous annual
   series.
@@ -229,9 +226,35 @@ until a governed operator import, provenance record and validation pass exist.
 - DHMV II DTM/DSM (Digitaal Vlaanderen): 1 m/5 m elevation based on 2013-2015
   LiDAR, suitable for elevation, slope and drainage. It does not provide water
   depth.
-- Waterinfo/VMM: station time series for water level, flow and precipitation.
-  These can describe hydrological state, but do not provide area-wide water
-  volume without a compatible bottom profile/bathymetry model.
+
+## Governed Waterinfo station history
+
+`scripts/provision_waterinfo_station_history.py` uses the public Waterinfo
+KiWIS query service only after an explicit operator command. It discovers the
+documented annual water-level (`192784`) and discharge (`192895`) groups,
+filters station points against the exact persisted Area and retains the raw
+station/value JSON plus SHA256 manifests.
+
+Each station and year becomes one immutable reference Dataset through the
+normal upload API. Series keys include the station identity; different stations
+are never averaged into one municipal value. Selection aggregation is a numeric
+mean over the selected station records and remains labelled as a point
+measurement. Water level or discharge does not establish area-wide water
+volume without compatible depth, profile and coverage data.
+
+## Governed historical orthophotos
+
+The bounded map acquisition registry includes the official annual winter
+mosaics for 2012-2025, period products for 2000-2003, 2005-2007 and 2008-2011,
+the RGB 1979-1990 summer mosaic and the panchromatic 1971 mosaic. Requests stay
+within the configured 128-1,024 m safety envelope and are persisted as
+EPSG:31370 raster Datasets with explicit product, layer, observation period,
+attribution and request hashes.
+
+Historical mosaics are for visual comparison only in this phase. Current YOLO
+building detection and current GRB QA remain restricted to `most_recent`, since
+validating an old image against today's building state would produce dishonest
+quality metrics.
 
 ## OSM