docs: Add v9.4 whats-new and changelog for alpha release

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: chrisgervang

docs/whats-new.md

@@ -4,10 +4,27 @@ This page contains highlights of each deck.gl release. Also check our [vis.gl bl
 
 ## deck.gl v9.4
 
+Release date: TBD
+
+### Controllers
+
+- New `doubleClickDragZoom` gesture on all controllers enables smooth zoom by double-clicking and dragging up/down.
+
+### GlobeView
+
+- [TerrainLayer](./api-reference/geo-layers/terrain-layer.md) now renders correctly on `GlobeView`, producing properly projected terrain meshes on the globe.
+- [TerrainExtension](./api-reference/extensions/terrain-extension.md) now supports `GlobeView`, enabling terrain-draped layers on the globe.
+- [Tile3DLayer](./api-reference/geo-layers/tile-3d-layer.md) renders correctly on `GlobeView`.
+
 ### Views
 
 - Views now support a `parameters` prop for per-view GPU draw state overrides. `GlobeView` uses this to enable back-face culling by default, and applications can override it with `new GlobeView({parameters: {cullMode: 'none'}})`.
 
+### Geo Layers
+
+- [TileLayer](./api-reference/geo-layers/tile-layer.md) now prioritizes tile requests closest to the viewport center, improving perceived load times during panning and zooming.
+- [TerrainLayer](./api-reference/geo-layers/terrain-layer.md) now correctly passes `zoomOffset` through to its child `TileLayer`.
+
 ### Performance
 
 - Picking in most instanced layers no longer allocates an `instancePickingColors` attribute buffer, instead using shader builtins `instance_index` / `gl_InstanceID`, reducing memory usage and initialization times.