Remove the weather and wind imagery fallbacks

Require engine.imagery for weather and wind and load the wind flow backend
from the layer manifest. Preserve Cesium's staging, frame retention, shell
ordering, wind fade and streamlines; Navara follows the same display policy.
Remove obsolete rendering modules and their three translated status keys.
Run every weather and wind display case on both the fake engine and the
headless Cesium engine, keeping the existing behavioural assertions.

Coupling: Cesium import files fall from 27 to 25, viewer lines from 1232 to
1177 and engine-name lines from 63 to 62. The explicit Cesium wind flow
backend deliberately raises renderer lines from 330 to 344 and extension
reads from 8 to 9; every other count stays unchanged.

Browser checks to run
GOOGLE_MAPS_API_KEY= CESIUM_ION_TOKEN= npm run dev -- --port 4291
node scripts/qa-contract-suite.mjs http://localhost:4291
node scripts/qa-weather-compare.mjs shoot http://localhost:4291 --out=qa-shots/weather-after

Compare weather and wind against the previous capture on both engines.

docs/GLOBE-PRIMITIVES.md

@@ -445,9 +445,9 @@ near the camera from one 8×8 atlas over the whole view.
 - **The wind field** (`src/layers/wind/render/display.js`): one image over
   the globe at order 20, faded with the camera's height while streamlines
   draw, raised at 5 km on 3D tiles. The streamlines stay each engine's,
-  behind the display's `flow` backend: Cesium's wind renderer without its
-  field (`rendering.js`, from the layer), Navara's flow mesh
-  (`render/navaraFlow.js`, from the manifest).
+  behind the display's `flow` backend, loaded by the manifest:
+  `render/cesiumFlow.js` supplies Cesium's streamlines (`rendering.js`),
+  and `render/navaraFlow.js` supplies Navara's flow mesh.
 - **The Bhote Koshi event imagery** (`src/layers/bhoteKoshi/render/display.js`):
   two `url` images over the event's rectangle at alpha 0.96, split left
   and right at the engine's split position, order 15. The event's and the