perf(terrain): one shared, cached and budgeted terrain height reader for Transit, Rail, Bike Share and local data

globe.getHeight is a ray cast against the drawn tile's mesh and
scene.sampleHeight a GPU depth render; several layers asked for them
uncached and unbudgeted. The cache written for Transit moves to
src/services/terrainSurface.js and is handed to every layer through the
ground service, so layers share one cache and one read budget.

- Rail reads each train on a ~4 m grid instead of every frame.
- Local data layers read terrain floors through it and stop depth samples
  at 8 ms a frame.
- Bike Share draws stations at once and finds their heights afterwards in
  4 ms steps.

Co-Authored-By: Claude Fable 5.2 <[email protected]>

scripts/package-boundaries.json

@@ -11,7 +11,8 @@
       "src/data/localGeojsonLod.js",
       "src/data/inputOwnership.js",
       "src/data/infrastructureOverlayEntry.js",
-      "src/sources/infrastructureData.js"
+      "src/sources/infrastructureData.js",
+      "src/services/terrainSurface.js"
     ],
     "external": ["cesium"]
   },
@@ -2056,6 +2057,7 @@
       "src/layers/bikeshare/state.js",
       "src/layers/bikeshare/testing.js",
       "src/layers/bikeshare/viewport.js",
+      "src/services/terrainSurface.js",
       "src/data/inputOwnership.js",
       "src/data/cameraSensitivity.js",
       "src/i18n/index.js",
@@ -3003,6 +3005,7 @@
       "src/search/placeSearch.js",
       "src/services/application.js",
       "src/services/groundFloor.js",
+      "src/services/terrainSurface.js",
       "src/services/groundSnap.js",
       "src/services/meshFloorSampler.js",
       "src/services/requests.js",
@@ -4034,6 +4037,7 @@
       "src/scopeMaskPolicy.js",
       "src/scopeMask.js",
       "src/services/groundFloor.js",
+      "src/services/terrainSurface.js",
       "src/data/routeSteps.js",
       "src/layers/directions/index.js",
       "src/data/pointerOwnerNames.js",
@@ -4378,6 +4382,7 @@
       "src/search/placeSearch.js",
       "src/services/application.js",
       "src/services/groundFloor.js",
+      "src/services/terrainSurface.js",
       "src/services/groundSnap.js",
       "src/services/meshFloorSampler.js",
       "src/services/requests.js",
@@ -5038,6 +5043,7 @@
       "src/renderGovernor.js",
       "src/services/application.js",
       "src/services/groundFloor.js",
+      "src/services/terrainSurface.js",
       "src/services/meshFloorSampler.js",
       "src/services/requests.js",
       "src/services/terrainHeights.js",
@@ -5082,6 +5088,7 @@
       "src/data/transitPresetStyle.js",
       "src/layers/transit/controls.js",
       "src/layers/transit/height.js",
+      "src/services/terrainSurface.js",
       "src/layers/transit/index.js",
       "src/layers/transit/ingestion.js",
       "src/layers/transit/lifecycle.js",