fix(styles): keep Snow wind sway bounded over time (#782)

The horizontal offset multiplied elapsed time by a sine, so flakes swung faster the longer the app ran. It is now the integral of the intended sway velocity, which stays bounded at any session age; Wind still scales the amplitude.

Co-authored-by: Sameh Khamis <[email protected]>

docs/CURRENT-STATE.md

@@ -1013,6 +1013,8 @@ and sharpen. Display supplies actions and renders settings; effect execution has
 no DOM dependency. Existing presets and the 500 ms transition remain unchanged.
 Stopping the controller revokes animation before asynchronous UI teardown; final
 destruction removes its stages and restores the borrowed bloom configuration.
+Snow's sideways sway stays within a fixed range at any session age; Wind scales
+its amplitude.
 
 ## Display control ownership