- Implement ElasticityPhysics struct with nodal assembly
- Two-phase assembly: element contributions then nodal accumulation
- Matrix-free CG solver using IterativeSolvers.jl
- Support for pressure boundary conditions
- Complete test: 190 nodes, 434 elements, converges in 430 iterations
- Max displacement 4.1 cm (cantilever beam validation)
- 476 lines including full documentation