fix(canvas): Multiple fixes for drag-drop, undo/redo, and code generation

Drag-drop fixes:
- Fix Objective default data: use nested 'source' object with extractor_id/output_name
- Fix Constraint default data: use 'type' field (not constraint_type), 'threshold' (not limit)

Undo/Redo fixes:
- Remove dependency on isDirty flag (which is always false due to auto-save)
- Record snapshots based on actual spec changes via deep comparison

Code generation improvements:
- Update system prompt to support multiple extractor types:
  * OP2-based extractors for FEA results (stress, displacement, frequency)
  * Expression-based extractors for NX model values (dimensions, volumes)
  * Computed extractors for derived values (no FEA needed)
- Claude will now choose appropriate signature based on user's description

studies/M1_Mirror/m1_mirror_flatback_lateral/3_results/optimization_summary.json

@@ -4,25 +4,25 @@
   "extraction_method": "ZernikeOPD_Annular",
   "inner_radius_mm": 135.75,
   "objectives_note": "Mass NOT in objective - WFE only",
-  "total_trials": 1,
-  "feasible_trials": 1,
+  "total_trials": 101,
+  "feasible_trials": 100,
   "best_trial": {
-    "number": 0,
-    "weighted_sum": 341.40717511411987,
+    "number": 76,
+    "weighted_sum": 220.12317796085603,
     "objectives": {
-      "wfe_40_20": 9.738648075724171,
-      "wfe_60_20": 24.138392317227122,
-      "mfg_90": 54.09444169121308,
-      "mass_kg": 102.89579477048632
+      "wfe_40_20": 7.033921022459454,
+      "wfe_60_20": 16.109562572565014,
+      "mfg_90": 32.457279654424745,
+      "mass_kg": 102.89579477048622
     },
     "params": {
-      "lateral_inner_u": 0.4,
-      "lateral_outer_u": 0.4,
-      "lateral_middle_pivot": 22.42,
-      "lateral_inner_angle": 31.96,
-      "lateral_outer_angle": 9.08
+      "lateral_inner_u": 0.40304412850085514,
+      "lateral_outer_u": 0.9043062289622721,
+      "lateral_middle_pivot": 25.869245488671304,
+      "lateral_inner_angle": 32.008659765295675,
+      "lateral_outer_angle": 13.952742709877848
     },
-    "iter_folder": "C:\\Users\\antoi\\Atomizer\\studies\\M1_Mirror\\m1_mirror_flatback_lateral\\2_iterations\\iter1"
+    "iter_folder": "C:\\Users\\antoi\\Atomizer\\studies\\M1_Mirror\\m1_mirror_flatback_lateral\\2_iterations\\iter77"
   },
-  "timestamp": "2026-01-13T11:01:22.360549"
+  "timestamp": "2026-01-13T18:41:14.992549"
 }

studies/M1_Mirror/m1_mirror_flatback_lateral/atomizer_spec.json

@@ -2,9 +2,9 @@
   "meta": {
     "version": "2.0",
     "created": "2026-01-17T15:35:12.034330Z",
-    "modified": "2026-01-17T15:35:12.034330Z",
+    "modified": "2026-01-20T18:24:29.805432Z",
     "created_by": "migration",
-    "modified_by": "migration",
+    "modified_by": "canvas",
     "study_name": "m1_mirror_flatback_lateral",
     "description": "Lateral support optimization with new U-joint expressions (lateral_inner_u, lateral_outer_u). Focus on WFE and MFG only - no mass objective.",
     "tags": [
@@ -104,10 +104,10 @@
       "expression_name": "lateral_outer_angle",
       "type": "continuous",
       "bounds": {
-        "min": 8.0,
-        "max": 17.0
+        "min": 8,
+        "max": 17
       },
-      "baseline": 9.08,
+      "baseline": 10,
       "units": "degrees",
       "enabled": true,
       "description": "Outer lateral support angle",