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/player.h

@@ -31,7 +31,7 @@
 #define PLAYER_DASH_SPEED    350.0f /* dash velocity (px/s)          */
 #define PLAYER_DASH_DURATION 0.15f  /* seconds the dash lasts        */
 #define PLAYER_DASH_MAX_CHARGES  3  /* max jetpack charges           */
-#define PLAYER_DASH_RECHARGE  3.0f  /* seconds to recharge one charge*/
+#define PLAYER_DASH_RECHARGE 30.0f  /* seconds to recharge one charge*/
 
 /* Jetpack boost (from powerup) */
 #define PLAYER_JETPACK_BOOST_DURATION 15.0f /* seconds the boost lasts    */