docs(changelog): add the #1721 fragment

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

changelog.d/1721-clouds-infrared-shader.md

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+- Satellite clouds on the 3D Tiles map apply their transparency in the shader
+  instead of rewriting each 4096 x 2048 image on the page, and changing the
+  cloud strength no longer builds a new image (mazy1998, #1721).