feat: Consolidates staff gump layouts (#2404)

## Summary
- Creates `PropsLayoutExtensions.cs` with reusable extension methods for both legacy `Gump` and `DynamicGumpBuilder` that encapsulate the repeating PropsConfig-style layout patterns (frame, header navigation, entry rows)
- Converts all 12 standardized staff gumps to use the new extensions, reducing ~570 lines of duplicated layout code
- Adds Type and Serial display to PropsGump and SkillsGump headers (e.g. `PlayerMobile (0x1)`)

### Extension methods provided
| Method | Pattern |
|--------|---------|
| `AddPropsFrame` | Background + offset region + origin coordinates |
| `AddPropsHeader` | 3-column: [Prev] [Title] [Next] |
| `AddPropsHeaderWithBack` | 4-column: [Back] [Title] [Prev] [Next] |
| `AddPropsEntryButton` | Label + action button |
| `AddPropsEntryNameValue` | Name + Value + action button |
| `AddPropsEntryTextInput` | Text input + action button |
| `AddPropsEntryLabel` | Label only (no button) |
| `AddPropsEntryType` | Full-width type label |
| `AddPropsEntryBlank` | Separator row |

### Gumps converted
PropsGump, GoGump, WhoGump, SkillsGump (frame+header), EditSkillGump, SetGump, SetObjectGump, SetPoint2DGump, SetPoint3DGump, SetTimeSpanGump (frame), SetListOptionGump (frame+header), CategorizedAddGump (frame+header)

## Test plan
- [x] Verify `[props` gump displays correctly with type + serial in header
- [x] Verify `[skills` gump displays correctly with type + serial in header
- [x] Verify `[go` navigation gump works (prev/next/back)
- [x] Verify property editing gumps (Set, SetObject, SetPoint2D, SetPoint3D, SetTimeSpan, SetListOption)
- [x] Verify `[categorizedadd` gump works
- [x] Verify `[who` gump works with pagination

Projects/UOContent/Gumps/Props/SetListOptionGump.cs

@@ -14,8 +14,6 @@ namespace Server.Gumps
 
         private const int TotalWidth = OffsetSize + EntryWidth + OffsetSize + SetWidth + OffsetSize;
 
-        private const int BackWidth = BorderSize + TotalWidth + BorderSize;
-
         private readonly object[] m_Values;
         protected Mobile m_Mobile;
         protected object m_Object;
@@ -48,52 +46,13 @@ namespace Server.Gumps
                     count = EntryCount;
                 }
 
-                var totalHeight = OffsetSize + (count + 2) * (EntryHeight + OffsetSize);
-                var backHeight = BorderSize + totalHeight + BorderSize;
-
-                AddBackground(0, 0, BackWidth, backHeight, BackGumpID);
-                AddImageTiled(BorderSize, BorderSize, TotalWidth, totalHeight, OffsetGumpID);
-
-                var x = BorderSize + OffsetSize;
-                const int y = BorderSize + OffsetSize;
-
-                const int emptyWidth = TotalWidth - PrevWidth - NextWidth - OffsetSize * 4;
-
-                AddImageTiled(x, y, PrevWidth, EntryHeight, HeaderGumpID);
-
-                if (page > 1)
-                {
-                    AddButton(
-                        x + PrevOffsetX,
-                        y + PrevOffsetY,
-                        PrevButtonID1,
-                        PrevButtonID2,
-                        0,
-                        GumpButtonType.Page,
-                        page - 1
-                    );
-                }
-
-                x += PrevWidth + OffsetSize;
-
-                AddImageTiled(x, y, emptyWidth, EntryHeight, HeaderGumpID);
-
-                x += emptyWidth + OffsetSize;
-
-                AddImageTiled(x, y, NextWidth, EntryHeight, HeaderGumpID);
-
-                if (page < pages)
-                {
-                    AddButton(
-                        x + NextOffsetX,
-                        y + NextOffsetY,
-                        NextButtonID1,
-                        NextButtonID2,
-                        0,
-                        GumpButtonType.Page,
-                        page + 1
-                    );
-                }
+                this.AddPropsFrame(TotalWidth, count + 2, out var x, out var y);
+                this.AddPropsHeader(
+                    TotalWidth, ref x, ref y, null,
+                    page > 1, 0, page < pages, 0,
+                    prevType: GumpButtonType.Page, prevParam: page - 1,
+                    nextType: GumpButtonType.Page, nextParam: page + 1
+                );
 
                 AddRect(0, prop.Name, 0);