Change region to use top-left and bottom-right coordinates

Replace center+delta region representation with a bounding box defined
by topLeft and bottomRight coordinate pairs, which maps more directly
to the visible map area.

https://claude.ai/code/session_0162emnCi1KxW5FkTNn2ZrvH

testHelpers/apolloTestServerHelpers.ts

@@ -27,10 +27,8 @@ const systemInfoForTesting: InterchangeSystemBuilderArguments = {
   useSelfUpdatingEtas: false,
   shuttleStopArrivalDegreeDelta: 0.001,
   initialRegion: {
-    latitude: 33.7937,
-    longitude: -117.8531,
-    latitudeDelta: 0.01,
-    longitudeDelta: 0.01,
+    topLeft: { latitude: 33.7987, longitude: -117.8581 },
+    bottomRight: { latitude: 33.7887, longitude: -117.8481 },
   },
 };