docs/FEM_ARCHITECTURE.md

# FEM Architecture - Vendor-Only Implementation

## 20-Step Empirical Testing & Build Plan

See full architecture document committed separately.

## Vendor Stack
- scikit-fem: FE assembly
- pygmsh: Mesh generation  
- meshio: I/O
- scipy.sparse: Linear algebra
- sympy: Symbolic math
- networkx: Topology
- pydantic: Validation

All code MUST use vendor APIs exclusively.