FIX: Resolve all paths to absolute before passing to NX

Root cause: Path.absolute() on Windows does NOT resolve '..' components.
sim_file_path was reaching NX as '...\studies\01_doe_landscape\..\..\models\Beam_sim1.sim'
NX likely can't resolve referenced parts from a path with '..' in it.

Fixes:
- nx_interface.py: glob from self.model_dir (resolved) not model_dir (raw)
- solver.py: sim_file.resolve() instead of sim_file.absolute()
- solve_simulation.py: os.path.abspath(sim_file_path) at entry point
- Diagnostic logging still in place for next run

projects/hydrotech-beam/studies/01_doe_landscape/_model_backup/README.md

@@ -0,0 +1,25 @@
+# Reference Models — Hydrotech Beam
+
+Golden copies of the NX model files. **Do not modify these directly.**
+
+Studies should copy these to their own `model/` folder and modify there.
+
+## Files
+
+| File | Description | Status |
+|------|-------------|--------|
+| `Beam.prt` | NX CAD part — sandwich I-beam with lightening holes | ⏳ Pending upload |
+| `Beam_fem1.fem` | FEM mesh file | ⏳ Pending upload |
+| `Beam_fem1_i.prt` | Idealized part for FEM | ⏳ Pending upload |
+| `Beam_sim1.sim` | Simulation file — SOL 101 static | ⏳ Pending upload |
+
+## Key Expression
+
+- `p173` — beam mass (kg)
+
+## Notes
+
+- ⏳ Awaiting Syncthing setup for project folder sync (dalidou ↔ server)
+- Model files will appear here once sync is live
+- Verify model rebuild across full design variable range before optimization
+- **Do NOT modify these reference copies** — studies copy them to their own `model/` folder