Add TODO: moon campaign with 3 levels and spacecraft transitions

TODO.md

@@ -30,6 +30,19 @@ exit counterpart.
 Implemented: base speed 120→200, accel 200→350, respawn 3→6s, stagger 0-3→0-8s,
 random horizontal drift (±60 px/s), moon level reduced from 24 to 8 asteroids.
 
+## Moon campaign: 3 levels with spacecraft transitions
+Extend the moon into a 3-level sequence connected by spacecraft takeoff/landing:
+- **moon01.lvl** — Current level. Exit triggers spacecraft takeoff, transitions
+  to moon02.
+- **moon02.lvl** — Second moon level (new terrain, new hazards). Starts with
+  spacecraft landing intro. Exit triggers takeoff to moon03.
+- **moon03.lvl** — Third/final moon level. Starts with spacecraft landing.
+  Exit triggers takeoff and transitions to level01 (space station).
+- **level01.lvl** (space station roof) — Starts with spacecraft landing on the
+  station rooftop. Ship stays landed (no takeoff). First armed level.
+- Moon exit transitions require the "spacecraft at level exit" feature so
+  the ship flies in when the player approaches the exit zone.
+
 ## Jetpack boost blue flame effects
 - Add continuous blue flame particles trailing from the player during jetpack
   boost (while boost is active, not just on burst)