feat(topology): Add Wedge 3D topology with Wedge6/Wedge15 aliases

New file implementing 3D wedge/prism topology:
- Wedge struct with dim=3, 6 corner nodes (triangular prism)
- reference_coordinates() with bottom triangle at z=-1, top at z=1
- edges() returns 9 edges (3 bottom + 3 top + 3 vertical)
- faces() returns 5 faces (2 triangular ends + 3 quadrilateral sides)
- Backward compatibility aliases: Wedge6 (linear), Wedge15 (quadratic)
- Zero-allocation tuple-based design

src/topology/wedges.jl

@@ -0,0 +1,131 @@
+# This file is a part of JuliaFEM.
+# License is MIT: see https://github.com/JuliaFEM/JuliaFEM.jl/blob/master/LICENSE
+
+"""
+    Wedge <: AbstractTopology
+
+Wedge/prism element topology (3D, triangular prism).
+
+**Important:** This type defines ONLY the geometric shape. Node count is determined
+by the interpolation scheme (basis functions):
+- `Lagrange{Wedge, 1}` → 6 nodes (linear)
+- `Lagrange{Wedge, 2}` → 15 nodes (quadratic, with edge midpoints)
+
+# Reference Element
+```
+      N6
+      /|\\
+     / | \\
+   N4-------N5
+    |  |   |
+    |  N3  |
+    | /  \\ |
+    |/    \\|
+   N1------N2
+```
+
+# Standard Corner Node Positions
+1-3: Bottom triangle
+4-6: Top triangle (directly above 1-3)
+
+# Topology Properties
+- Dimension: 3
+- Corner nodes: 6
+- Edges: 9
+- Faces: 5 (2 triangles + 3 quads)
+
+**Zero allocation:** All functions return compile-time sized tuples.
+
+See also: [`AbstractTopology`](@ref), [`Pyramid`](@ref)
+"""
+struct Wedge <: AbstractTopology end
+
+dim(::Wedge) = 3
+
+"""
+    reference_coordinates(::Wedge)
+
+Get corner node positions for Wedge (6 vertices).
+"""
+function reference_coordinates(::Wedge)
+    return (
+        (0.0, 0.0, -1.0),  # Node 1: Bottom triangle
+        (1.0, 0.0, -1.0),  # Node 2: Bottom triangle
+        (0.0, 1.0, -1.0),  # Node 3: Bottom triangle
+        (0.0, 0.0, 1.0),  # Node 4: Top triangle
+        (1.0, 0.0, 1.0),  # Node 5: Top triangle
+        (0.0, 1.0, 1.0),  # Node 6: Top triangle
+    )
+end
+
+"""
+    edges(::Wedge)
+
+Edge connectivity for wedge (corner nodes).
+"""
+function edges(::Wedge)
+    return (
+        (1, 2), (2, 3), (3, 1),  # Bottom triangle edges
+        (4, 5), (5, 6), (6, 4),  # Top triangle edges
+        (1, 4), (2, 5), (3, 6),  # Vertical edges
+    )
+end
+
+"""
+    faces(::Wedge)
+
+Face connectivity for wedge (2 triangular + 3 quadrilateral faces).
+"""
+function faces(::Wedge)
+    return (
+        (1, 3, 2),        # Face 1: Bottom triangle
+        (4, 5, 6),        # Face 2: Top triangle
+        (1, 2, 5, 4),     # Face 3: Quad
+        (2, 3, 6, 5),     # Face 4: Quad
+        (3, 1, 4, 6),     # Face 5: Quad
+    )
+end
+
+# ============================================================================
+# Deprecated aliases (for backwards compatibility)
+# ============================================================================
+
+"""
+    Wedge6
+
+**DEPRECATED:** Backward compatibility alias. Use `Wedge` with `Lagrange{Wedge, 1}`.
+
+This alias allows old code to work:
+```julia
+# Old style (still works)
+element = Element(Wedge6, (1, 2, 3, 4, 5, 6))
+# Internally converted to:
+element = Element(Wedge, (1, 2, 3, 4, 5, 6))  # Infers Lagrange{Wedge, 1}
+```
+
+New code should use explicit topology + basis:
+```julia
+element = Element(Lagrange{Wedge, 1}, (1, 2, 3, 4, 5, 6))
+```
+"""
+const Wedge6 = Wedge
+
+"""
+    Wedge15
+
+**DEPRECATED:** Backward compatibility alias. Use `Wedge` with `Lagrange{Wedge, 2}`.
+
+This alias allows old code to work:
+```julia
+# Old style (still works)
+element = Element(Wedge15, (1, 2, ..., 15))
+# Internally converted to:
+element = Element(Wedge, (1, 2, ..., 15))  # Infers Lagrange{Wedge, 2}
+```
+
+New code should use explicit topology + basis:
+```julia
+element = Element(Lagrange{Wedge, 2}, (1, 2, ..., 15))
+```
+"""
+const Wedge15 = Wedge  # Same topology! Node count from basis.