Horizon area sprites + shield-less exterior area (#22594)

Fills in a lot of the blanks in the area icon states on the Horizon with
new sprites. Looks neater in SDMM.

Adds a new exterior/no_shields area, which is exclusively used for the
wings and around the starboard thrusters, around which shields will not
generate. This is pulled off in what I hope is a non-demanding way. This
is used to resolve that funny issue with starboard propulsion's wide
arcing shield, and to force shields on D3 to be taut to the walls.

The regular exterior area is retained wherever we want there to be
shields around EVA catwalks.

<img width="1080" height="1080" alt="image"
src="https://github.com/user-attachments/assets/4826b32f-34e2-44ab-b0be-f9fee9622fc8"
/>

<img width="1056" height="896" alt="image"
src="https://github.com/user-attachments/assets/cde72fa6-41eb-4c2a-b843-9959359ca505"
/>

code/modules/shieldgen/shield_gen_external.dm

@@ -30,15 +30,15 @@
 	for (var/tt in RANGE_TURFS(field_radius, gen_turf))
 		T = tt
 		// Ignore station areas.
-		if (GLOB.the_station_areas[T.loc] || is_shuttle_area(T.loc))
+		if ((GLOB.the_station_areas[T.loc] && !is_shieldless_exterior(T.loc)) || is_shuttle_area(T.loc))
 			continue
-		else if (istype(T, /turf/space) || istype(T, /turf/simulated/floor/exoplanet/asteroid) || isopenturf(T) || istype(T, /turf/simulated/floor/reinforced))
+		else if (istype(T, /turf/space) || isopenturf(T) || istype(T, /turf/simulated/floor/reinforced))
 			for (var/uu in RANGE_TURFS(1, T))
 				U = uu
 				if (T == U)
 					continue
 
-				if (GLOB.the_station_areas[U.loc] || istype(U, /turf/simulated/mineral/surface))
+				if (GLOB.the_station_areas[U.loc] && !is_shieldless_exterior(U.loc))
 					out += T
 					break
 
@@ -52,19 +52,21 @@
 		if(below)
 			for(var/turf/z as anything in below)
 				connected_levels += z
+
 		for(var/turf/z in connected_levels)
 			for (var/tt in RANGE_TURFS(field_radius, z))
 				T = tt
 				// Ignore station areas.
-				if (GLOB.the_station_areas[T.loc] || istype(T.loc, /area/shuttle))
+				if ((GLOB.the_station_areas[T.loc] && !is_shieldless_exterior(T.loc)) || istype(T.loc, /area/shuttle))
 					continue
-				else if (istype(T, /turf/space) || istype(T, /turf/simulated/floor/exoplanet/asteroid) || isopenturf(T) || istype(T, /turf/simulated/floor/reinforced))
+
+				else if (istype(T, /turf/space) || isopenturf(T) || istype(T, /turf/simulated/floor/reinforced))
 					for (var/uu in RANGE_TURFS(1, T))
 						U = uu
 						if (T == U)
 							continue
 
-						if (GLOB.the_station_areas[U.loc])
+						if (GLOB.the_station_areas[U.loc] && !is_shieldless_exterior(U.loc))
 							out += T
 							break
 	return out

code/modules/turbolift/turbolift_areas.dm

@@ -1,6 +1,7 @@
 // Used for creating the exchange areas.
 /area/turbolift
 	name = "Turbolift"
+	icon_state = "turbolift"
 	base_turf = /turf/simulated/open
 	requires_power = 0
 	station_area = TRUE