- scan_existing_fea_results() scans study for existing OP2/F06 files
- Introspection now returns existing_fea_results with recommended source
- New POST /nx/extract endpoint runs extractors on existing OP2 files
- Supports: displacement, stress, frequency, mass_bdf, zernike
- No NX solve needed - uses PyNastran and Atomizer extractors directly
This allows users to test extractors and get physics data from existing
simulation results without re-running the FEA solver.