Winter: real flowing wind (curved streamlines)…

Details

The straight diagonal 'gust' dashes read as rain. Replace them with
genuine wind: each wind wisp now records a streamline trail through the
curl-noise flow field and renders as a curving ribbon that fades tail->
head — so the wind visibly sweeps and swirls (igloo-style) instead of
falling like rain.
- Add per-particle trail history (wind particles only); cleared on
  recycle/wrap so ribbons never streak across teleports.
- Winter flow: more curl than base wind so streamlines clearly curve.
- More, brighter, longer wind streamlines; visible on dark and cream.
- Cut sleet entirely and made rain a rare brief shower, so winter reads
  as snowy + windy rather than rainy.
Winter ~57fps (other seasons unchanged at 60); build passes.

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