Add TODO: elevator and teleporter level transition styles

TODO.md

@@ -154,3 +154,12 @@ subtle, low-alpha, and layered behind/in front of the player for depth.
 The spacecraft fly-in animation should only play on surface levels (moon01,
 mars01, etc.). Interior/base levels (mars02, mars03, generated mars_base,
 generated station) should skip it — the player is already indoors.
+
+## New level transition styles: elevator and teleporter
+Two new transition animations to complement the spacecraft fly-in:
+- **Elevator** — Doors slide shut, brief pause (screen shake / rumble),
+  doors slide open onto the new level. Good for base/station interior
+  transitions (mars02 → mars_base, between generated station levels).
+- **Teleporter** — Energy charge-up effect around the player, flash/warp
+  distortion, player materialises in the new level. Good for cross-planet
+  jumps or generated-to-handcrafted transitions.