Dedicated Mars Base generator with 6 segment types (entry, shaft, corridor,
turret hall, hive, arena), depth-scaled difficulty, and exit to boss arena
after 2 generated levels. Mars themes integrated into all 7 generic segment
generators. Full level chain: moon03 → mars01 → mars02 → mars_base (×2) →
mars03 → station.
Also: jetpack fuel pickup preserves recharge progress, depth counters reset
on game loop, NULL checks on entity spawns, charger charge timeout, bg
decoration in Mars Base generator.
Distance-based sound effects with stereo panning for explosions, impacts,
and pickups. Spacecraft entity with full state machine (fly-in, land, take
off, fly-out), engine/synth sound loops, thruster particles, and PNG
spritesheet. Moon level intro defers player spawn until ship lands.
Also untrack build/ objects that were committed by mistake.
