Add jetpack fuel pickup and slow base recharge to 30s

Jetpack charges now take 30s to passively recharge (up from 3s),
making fuel management a core gameplay loop. A new fuel canister
powerup (POWERUP_FUEL) restores exactly one charge on pickup.

The existing jetpack powerup remains as the rare full-refill + 15s
boost. Fuel pickups replace most procedural jetpack spawns at higher
spawn rates to compensate for the weaker per-pickup value. Fuel
canisters also appear in corridors and arenas.

Adds orange canister pixel art, editor icon, entity registry entry,
and places fuel pickups throughout moon01.

src/game/editor.c

@@ -253,6 +253,8 @@ static const uint64_t s_icon_bitmaps[ICON_COUNT] = {
     0x006C7E7E3E1C0800ULL,
     /* ICON_BOLT: lightning bolt */
     0x0C1C18387060C000ULL,
+    /* ICON_FUEL: fuel canister */
+    0x003C4242423C1800ULL,
     /* ICON_DRONE: quad-rotor */
     0x00427E3C3C7E4200ULL,
     /* ICON_GUN: pistol shape */