Si'akh Flame Priest Robes (#19055)

Adds robes of Si'akh flame priests to the Unathi Loadout. These robes
are basically the same as the Sk'akh ones, but they lack the gilded
chains and ornamentation, and have different descriptions to match the
ascetic nature of their faith.

Worn sprite

![image](https://github.com/Aurorastation/Aurora.3/assets/30341877/2b1deeb2-9e28-481b-8982-f87e3923580d)

in-hand sprite

![image](https://github.com/Aurorastation/Aurora.3/assets/30341877/7504f180-e831-4e23-b83f-4122e62307a6)

code/modules/client/preference_setup/loadout/items/xeno/unathi.dm

@@ -464,7 +464,7 @@
 	cost = 1
 	whitelisted = list(SPECIES_UNATHI)
 	sort_category = "Xenowear - Unathi"
-	allowed_roles = list("Chaplain")
+	allowed_roles = list("Chaplain", "Off-Duty Crew Member")
 	flags = GEAR_HAS_NAME_SELECTION | GEAR_HAS_DESC_SELECTION
 
 /datum/gear/uniform/unathi/skakh/New()
@@ -475,3 +475,12 @@
 	robes["Sk'akh healer's robes"] = /obj/item/clothing/under/unathi/skakh/healer
 	robes["Sk'akh warrior's robes"] = /obj/item/clothing/under/unathi/skakh/warrior
 	gear_tweaks += new /datum/gear_tweak/path(robes)
+
+/datum/gear/uniform/unathi/siakh
+	display_name = "Siakh robes"
+	path = /obj/item/clothing/under/unathi/siakh
+	cost = 1
+	whitelisted = list(SPECIES_UNATHI)
+	sort_category = "Xenowear - Unathi"
+	allowed_roles = list("Chaplain", "Off-Duty Crew Member")
+	flags = GEAR_HAS_NAME_SELECTION | GEAR_HAS_DESC_SELECTION