## Summary
- always wrap NWN model compilation with `xvfb-run`, even when the caller has `DISPLAY`
- fail closed with an actionable error when `xvfb-run` is unavailable instead of opening the client UI
- update the compiler contract and regression coverage
## Verification
- focused red/green regression tests
- `nix develop -c make check`
- real NWN compile with `DISPLAY=:0` under transient Xvfb; binary MDL output verified
Generated with Claude CodeReviewed-on: #49
Co-authored-by: vickydotbat <vickydotbat@tutamail.com>
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