Improve particle wind animation: longer lifetimes, wind-scaled count, zoom scatter

- MAX_AGE 8s → 25s: particles live much longer, drastically less twinkle
- activeN scales 60→300 with wind speed (0–25 kt): calm = sparse drift,
  strong wind = dense streaks
- Zoom-out detection: scatter() fires immediately when latRange grows >1.8×,
  instantly filling the new viewport instead of waiting for old particles to die
- Alpha uses sine curve (sin(π·age/MAX_AGE)) instead of linear fade:
  particles ease in from birth, peak at mid-life, and ease out — no bright
  birth flash that caused the twinkle effect

https://claude.ai/code/session_01HXPjBsogsJVRwCiekDGkJX

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