Add ground fills to the globe contract

engine.ground draws sets of polygons (with holes), discs, cells and
corridors draped on the surface, with fill and outline colours, order and
picks, written in bulk and committed. Every engine implements it:

- Cesium batches each set into one GroundPrimitive for fills and one
  GroundPolylinePrimitive for outlines and pixel corridors, classified
  against terrain and 3D tiles; sets that are not pickable stay out of the
  pick pass.
- Navara draws them in one screen pass after tone mapping that finds each
  pixel's ground from the scene depth and tests the items in its screen
  cell; long rings are split into edge bins. Measured at Dubai against
  SDK vector layers, the pass matched Cesium's frame time up to 10,000
  polygons with a few megabytes instead of 70 to 146, drew exact colours
  and outlines, and hid reliably across an engine switch, where vector
  layers hidden with update({ show: false }) never hid. Dense corridors
  remain its limit (10,000 cost 135 ms a frame).
- The fake engine keeps the same registry and CPU picks.

The contract suite checks it on both engines (Cesium 66/66, Navara 69/69).
Earthquakes and fire perimeters have unwired ground prototypes whose
drawing matches today's Cesium one (0.998 on Cesium, 0.976 on Navara).
docs/GLOBE-PRIMITIVES.md describes the primitives and when to use each.

docs/CURRENT-STATE.md

@@ -183,10 +183,25 @@ one application, and only the globe-bound parts move to the next engine.
   `node scripts/qa-contract-suite.mjs <origin>` runs them in headless Chrome
   on the real Cesium and Navara of a keyless dev server, with a real pointer
   and real canvases; checks of state the app drives itself (contact sonar)
-  are skipped and named. On November 7, 2026 Cesium passed 63 of 63 and
-  Navara 66 of 66. `movers` and `lines` are required of every engine: Cesium
+  are skipped and named. On November 7, 2026 Cesium passed 66 of 66 and
+  Navara 69 of 69. `movers` and `lines` are required of every engine: Cesium
   draws them with billboards, points, models and polyline primitives
   (`src/globe/cesium/movers.js`, `lines.js`).
+- **Fills on the ground** (`engine.ground`) are required of every engine
+  too. They come in sets of polygons with holes, discs, lon/lat cells or
+  corridors (a width in px or m), draped over terrain and 3D tiles. Each
+  item has its own fill, outline and `pickId`. A set has a draw `order`, and
+  shows, hides and replaces its items in bulk.
+  - Cesium draws them with batched `GroundPrimitive` and
+    `GroundPolylinePrimitive`.
+  - Navara draws them in one screen pass classified on the scene depth
+    (`src/globe/navara/ground/`).
+  - Navara's vector layers were measured against that pass and lost
+    (`docs/GLOBE-PRIMITIVES.md`).
+  - No layer draws through `engine.ground` yet. Earthquakes and fire
+    perimeters have prototypes in `render/ground.js`.
+  - On November 7, 2026, `scripts/qa-ground-suite.mjs` (the ground checks
+    with pixels) passed 3 of 3 on both engines.
 - **Engine coupling.** `node scripts/report-engine-coupling.mjs` counts the
   engine-specific code outside the engines: renderer lines per engine, Cesium
   imports, `viewer` mentions, engine-name checks, raw Navara reads, Navara