Weather: clouds, storms and lightning 8c11d77

The R toggle just grew a full weather ladder. Where it once flipped CLEAR/RAIN it now steps through five states — MISSION DEFAULT → CLEAR → CLOUDS → RAIN → STORM — on the main menu, on the plane-select map, and saved between visits:

1. CLOUDS breaks the original’s cloudless sky — the scattered sprite deck that ships with the sim finally gets to fly, fading in over a couple of seconds with a light dimming of the day. Everything eases; nothing pops.
2. RAIN implies overcast now — the streak rain you know, under the cloud deck, with the usual gloom dragging the murk in close.
3. STORM brings the lightning. Every few seconds a jagged channel bolt walks down out of the deck somewhere within a few miles, the whole sky answers with a cold blue-white flash, and the thunder arrives late — delayed by true distance at 343 m/s, a crack decaying into a long low rumble through the audio graph.
4. Clouds got their own weather channel — separate from the rain blend, so overcast days can exist without a drop of rain, and every state fades smoothly through the same sky/fog/sun gloom the rain always used.
5. Manners kept: satellite planning maps stay free of rain, murk and bolts; pausing still silences the sky; and missions you authored stay exactly as clear as you left them — MISSION DEFAULT never surprises you.