Lakes fill only to their lower rim and keep clear of spawn and the dock (t96)

The lake lip was Math.min(surfY), the highest ground (y grows downward), so water was poured
above the lower rim and, once levelled, ran up to the trade dock on 4 of 12 seeds. The lip is
now the lower rim edge minus one, and each lake stays 80 grains from spawn. Seed hashes and
the shallow-ore hash re-baselined (changes only under lake basins); golden fixtures also
freeze surfY/dirtY/AMB from the previous generator.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/t_lakes.py

@@ -47,7 +47,7 @@ with launch(viewport={'width':1280,'height':760}) as (_, pg, url):
         pools=pg.evaluate(measure)
         assert pools and all(p['max']-p['min']<=1 for p in pools),pools
         print(state,result,pools,flush=True)
-        assert result['n']>300 and result['hi']-result['lo']<=1 and result['wet']==0
+        assert result['n']>150 and result['hi']-result['lo']<=1 and result['wet']==0
         pg.evaluate('snapCamera();renderDirty.fill(1);')
         pg.wait_for_timeout(300)
         pg.screenshot(path=str(ROOT/f'shots/t96-{state}-settled.png'))