chore(scripts): Add docs quickstart regression verifier

Activates the repo project, includes the minimal elasticity snippet, and
errors unless assembled ndofs and stiffness nnz match locked doc values.

- Expected (375, 19773); for Documentation CI / local checks

scripts/verify_docs_quickstart.jl

@@ -0,0 +1,16 @@
+#!/usr/bin/env julia
+# Verify the Documenter minimal elasticity snippet (repository root).
+#   julia --project=. scripts/verify_docs_quickstart.jl
+
+const ROOT = dirname(@__DIR__)
+
+using Pkg
+Pkg.activate(ROOT)
+Pkg.instantiate()
+
+include(joinpath(ROOT, "docs", "src", "snippets", "minimal_elasticity_quickstart.jl"))
+r = minimal_elasticity_quickstart()
+if r.ndofs != 375 || r.nnz_stiffness != 19773
+    error("quickstart regression: expected (375, 19773), got ($(r.ndofs), $(r.nnz_stiffness))")
+end
+println("verify_docs_quickstart.jl: OK")