feat: replace digitized flood zones with owner-traced polygons

The 7 Chiang Mai inundation zones are now hand-traced by the project
owner against the real basemap (cnx_flood.geojson), replacing the
scan-digitized approximation and its georeferencing error entirely.
Features are ordered zone 7 -> 1 so the earlier-flooding (smaller)
zones render on top of the wider extents in Leaflet.

src/static/flood-zones-p1.geojson

@@ -1 +1 @@
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