feat: Add E11 Part Mass extractor, document pyNastran mass accuracy issue

New E11 Part Mass Extractor:
- Add nx_journals/extract_part_mass_material.py - NX journal using
  NXOpen.MeasureManager.NewMassProperties() for accurate geometry-based mass
- Add optimization_engine/extractors/extract_part_mass_material.py - Python
  wrapper that reads JSON output from journal
- Add E11 entry to extractors/catalog.json

Documentation Updates:
- SYS_12_EXTRACTOR_LIBRARY.md: Add mass accuracy warning noting pyNastran
  get_mass_breakdown() under-reports ~7% on hex-dominant meshes with
  tet/pyramid fill elements. E11 (geometry .prt) should be preferred over
  E4 (BDF) unless material is overridden at FEM level.
- 01_CHEATSHEET.md: Add mass extraction tip

V14 Config:
- Expand design variable bounds (blank_backface_angle max 4.5°,
  whiffle_triangle_closeness max 80mm, whiffle_min max 60mm)

Testing showed:
- E11 from .prt: 97.66 kg (accurate - matches NX GUI)
- E4 pyNastran get_mass_breakdown(): 90.73 kg (~7% under-reported)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.claude/skills/01_CHEATSHEET.md

@@ -49,6 +49,9 @@ requires_skills:
 | Zernike builder | E10 | `ZernikeObjectiveBuilder(op2_finder)` |
 | Part mass + material | E11 | `extract_part_mass_material(prt_file)` → mass, volume, material |
 
+> **Mass extraction tip**: Always use E11 (geometry .prt) over E4 (BDF) for accuracy.
+> pyNastran under-reports mass ~7% on hex-dominant meshes with tet/pyramid fills.
+
 **Full details**: See `SYS_12_EXTRACTOR_LIBRARY.md` or `modules/extractors-catalog.md`
 
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