feat: add adaptive isogrid tool — project foundations

- Python Brain: density field, constrained Delaunay triangulation,
  pocket profiles, profile assembly, validation modules
- NX Hands: skeleton scripts for geometry extraction, AFEM setup,
  per-iteration solve (require NX environment to develop)
- Atomizer integration: 15-param space definition, objective function
- Technical spec, README, sample test geometry, requirements.txt
- Architecture: Python Brain + NX Hands + Atomizer Manager

tools/adaptive-isogrid/src/nx/__init__.py

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+"""
+Adaptive Isogrid — NX Hands
+
+NXOpen journal scripts for geometry extraction, AFEM setup, and per-iteration solve.
+These scripts run inside NX Simcenter via the NXOpen Python API.
+"""

tools/adaptive-isogrid/src/nx/build_interface_model.py

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+"""
+NXOpen script — Build Interface Model (Model A) for Assembly FEM.
+
+ONE-TIME: Creates spider elements (RBE2/RBE3) at each hole + edge BC nodes.
+Exports interface_nodes.json for the iteration script.
+
+NOTE: Skeleton — requires NX environment for development.
+See docs/technical-spec.md Section 4.2 for full pseudocode.
+"""
+
+
+def build_interface_model(geometry_json_path, fem_part):
+    """
+    Build Model A: spider elements at each hole + edge BC nodes.
+    
+    For each hole:
+    - Center node (master)
+    - N circumference nodes (~1 per 2mm of circumference)
+    - RBE2 (rigid) or RBE3 (distributing) spider
+    
+    For plate boundary:
+    - Edge nodes at ~3mm spacing
+    
+    Exports interface_nodes.json with all node IDs and coordinates.
+    """
+    raise NotImplementedError(
+        "Develop inside NX Simcenter. See docs/technical-spec.md Section 4.2."
+    )

tools/adaptive-isogrid/src/nx/extract_geometry.py

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+"""
+NXOpen script — Extract plate geometry from selected face.
+
+ONE-TIME: Run inside NX. User selects plate face, assigns hole weights.
+Exports geometry.json for the Python brain.
+
+NOTE: This is pseudocode / skeleton. Actual NXOpen API calls need
+NX environment to develop and test.
+"""
+
+# This script runs inside NX — NXOpen is available at runtime
+# import NXOpen
+# import json
+# import math
+
+
+def extract_plate_geometry(face, hole_weights):
+    """
+    Extract plate geometry from an NX face.
+    
+    Parameters
+    ----------
+    face : NXOpen.Face
+        The selected plate face.
+    hole_weights : dict
+        {loop_index: weight} from user input.
+    
+    Returns
+    -------
+    dict : geometry definition for export.
+    """
+    raise NotImplementedError(
+        "This script must be developed and tested inside NX Simcenter. "
+        "See docs/technical-spec.md Section 2 for full pseudocode."
+    )
+
+
+def sample_edge(edge, tolerance=0.1):
+    """Sample edge curve as polyline with given chord tolerance."""
+    # NXOpen: edge.GetCurve(), evaluate at intervals
+    raise NotImplementedError
+
+
+def fit_circle(points):
+    """Fit a circle to boundary points. Returns (center, diameter)."""
+    # Least-squares circle fit
+    raise NotImplementedError
+
+
+def export_geometry(geometry, filepath='geometry.json'):
+    """Export geometry dict to JSON."""
+    import json
+    with open(filepath, 'w') as f:
+        json.dump(geometry, f, indent=2)

tools/adaptive-isogrid/src/nx/iteration_solve.py

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+"""
+NXOpen script — Per-iteration Model B rebuild + solve + extract.
+
+LOOP: Called by Atomizer for each trial.
+1. Delete old Model B geometry + mesh
+2. Import new 2D ribbed profile from rib_profile.json
+3. Mesh with hard-point seeds at interface node locations
+4. Merge nodes in Assembly FEM
+5. Solve (Nastran)
+6. Extract results → results.json
+
+NOTE: Skeleton — requires NX environment for development.
+See docs/technical-spec.md Section 4.3 for full pseudocode.
+"""
+
+
+def iteration_solve(profile_path, interface_nodes_path, afem_part):
+    """
+    Single optimization iteration.
+    
+    Returns dict with status, mass, stress/displacement fields.
+    """
+    raise NotImplementedError(
+        "Develop inside NX Simcenter. See docs/technical-spec.md Section 4.3."
+    )
+
+
+def extract_results(afem, solution):
+    """
+    Extract field results from solved assembly FEM.
+    Only from Model B elements (plate mesh), ignoring spiders.
+    """
+    raise NotImplementedError(
+        "Develop inside NX Simcenter. See docs/technical-spec.md Section 4.3."
+    )