feat(topology): Add type-level nnodes() method

- Add nnodes(::Type{<:AbstractTopology{N}}) method for type queries
- Enables compile-time node count without instantiation
- Example: nnodes(Triangle{3}) returns 3
- Complements existing instance method for dispatch consistency

src/topology/api.jl

@@ -177,6 +177,22 @@ Concrete types inherit this implementation automatically.
 """
 nnodes(::AbstractTopology{N}) where N = N
 
+"""
+    nnodes(::Type{<:AbstractTopology{N}}) -> Int
+
+Number of nodes for a topology type (compile-time constant from type parameter).
+
+# Examples
+
+```julia
+nnodes(Triangle{3})   # 3
+nnodes(Triangle{6})   # 6
+nnodes(Quadrilateral{4})  # 4
+nnodes(Quadrilateral{9})  # 9
+```
+"""
+nnodes(::Type{<:AbstractTopology{N}}) where N = N
+
 """
     dim(topology::AbstractTopology) -> Int