fix: shift flood zones 1.05 km south, anchored to Nawarat Bridge

The P.1 marker (Nawarat Bridge, 18.7875) sat inside zone 2 near its top
edge, but the bridge IS Chang Khlan's northern boundary - the layer was
~0.0095 deg too far north (the district-centroid correction in c4e0fb6
overshot). Zone 2's north edge now lands at the bridge.

src/static/flood-zones-p1.geojson

@@ -1 +1 @@
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