fix: NPC outfits no longer stack two items on one layer (#2715)

Companion to #2712, which covers HireRanger's refused `EquipItem`. A sweep that built every constructible Mobile 2,000 times under each expansion found these other outfits that put two items on one layer. They don't leak, because `AddItem` skips `CheckEquip`, but the NPC wears both items and the client draws only one.

| NPC | Conflict |
|---|---|
| Miner, Ranger, Thief | Own shirt/pants/ThighBoots added on top of the random `BaseVendor.InitOutfit` (shoes doubled on every spawn) |
| MasterTheophilus | Shoes + Robe added over `EvilMageLord`'s Sandals + Robe |
| Merchant | Shirt + FancyShirt, or PlainDress + FancyDress |
| IronWorker | Bandana/JesterHat + Bascinet |
| MeerCaptain | One-handed sword + Crossbow |
| BakeKitsune | `BodyMod` isn't saved, so after a restart `RemoveDisguise` bailed and the next `Disguise()` stacked a second robe and pair of shoes |

## Changes
- `BaseCreature.ReplaceEquipment(item)` equips an item in place of whatever an inherited outfit put on its layer, and deletes the item if it still can't be equipped.
- Miner, Ranger, Thief, MasterTheophilus: their own pieces replace the inherited ones.
- Merchant and IronWorker: dropped the duplicate roll. Each kept the item the client was already drawing, which is the last one sent: the fancy set and the Bascinet.
- MeerCaptain: the sword goes into its pack as loot. **Behavior change:** `Mobile.Weapon` checks the one-handed layer first, so it was fighting with the sword despite its archer AI, its Archery skill and the bolts in its pack. It now uses the crossbow.
- BakeKitsune: `RemoveDisguise` strips the disguise without checking `IsBodyMod`.

## Testing
- I re-ran the sweep (local diagnostic, not committed; needs client tiledata) at 500 rolls × 12 expansions. Only HireRanger (#2712) and LordOaks (separate fix coming) remain.
- UOContent.Tests: 1218 passed, 2 skipped.

Projects/UOContent/Mobiles/BaseCreature.cs

@@ -5724,6 +5724,20 @@ namespace Server.Mobiles
             }
         }
 
+        /// <summary>
+        ///     Equips <paramref name="item" /> in place of whatever an inherited outfit put on its layer.
+        ///     AddItem would stack both on one layer, and EquipItem would refuse and orphan the item.
+        /// </summary>
+        public void ReplaceEquipment(Item item)
+        {
+            FindItemOnLayer(item.Layer)?.Delete();
+
+            if (!EquipItem(item))
+            {
+                item.Delete();
+            }
+        }
+
         public virtual void HealStart(Mobile patient)
         {
             StopHeal();