fix(canvas): Add Save/Reload buttons and expand IntrospectionPanel to show all model data

CanvasView:
- Fix Save button visibility - now shows when spec is loaded (grayed if no changes)
- Separate logic for spec mode vs legacy mode save buttons
- Fix Reload button visibility

IntrospectionPanel:
- Add Mass Properties section (mass, volume, surface area, CoG, body count)
- Add Linked Parts section showing file dependencies
- Add Bodies section (solid/sheet body counts)
- Add Units section showing unit system
- Type-safe access to all nested properties

atomizer-dashboard/frontend/src/pages/CanvasView.tsx

@@ -296,17 +296,34 @@ export function CanvasView() {
 
         {/* Action Buttons */}
         <div className="flex items-center gap-2">
-          {/* Save Button - only show when there's a study and changes */}
-          {activeStudyId && (
+          {/* Save Button - always show in spec mode with study, grayed when no changes */}
+          {useSpecMode && spec && (
             <button
               onClick={saveToConfig}
-              disabled={isSaving || (useSpecMode ? !specIsDirty : !hasUnsavedChanges)}
+              disabled={isSaving || !specIsDirty}
               className={`px-3 py-1.5 text-sm rounded-lg transition-colors flex items-center gap-1.5 ${
-                (useSpecMode ? specIsDirty : hasUnsavedChanges)
+                specIsDirty
                   ? 'bg-green-600 hover:bg-green-500 text-white'
                   : 'bg-dark-700 text-dark-400 cursor-not-allowed border border-dark-600'
               }`}
-              title={(useSpecMode ? specIsDirty : hasUnsavedChanges) ? `Save changes to ${useSpecMode ? 'atomizer_spec.json' : 'optimization_config.json'}` : 'No changes to save'}
+              title={specIsDirty ? 'Save changes to atomizer_spec.json' : 'No changes to save'}
+            >
+              <Save size={14} />
+              {isSaving ? 'Saving...' : 'Save'}
+            </button>
+          )}
+          
+          {/* Legacy Save Button */}
+          {!useSpecMode && activeStudyId && (
+            <button
+              onClick={saveToConfig}
+              disabled={isSaving || !hasUnsavedChanges}
+              className={`px-3 py-1.5 text-sm rounded-lg transition-colors flex items-center gap-1.5 ${
+                hasUnsavedChanges
+                  ? 'bg-green-600 hover:bg-green-500 text-white'
+                  : 'bg-dark-700 text-dark-400 cursor-not-allowed border border-dark-600'
+              }`}
+              title={hasUnsavedChanges ? 'Save changes to optimization_config.json' : 'No changes to save'}
             >
               <Save size={14} />
               {isSaving ? 'Saving...' : 'Save'}
@@ -314,7 +331,7 @@ export function CanvasView() {
           )}
 
           {/* Reload Button */}
-          {activeStudyId && (
+          {(useSpecMode ? spec : activeStudyId) && (
             <button
               onClick={handleReload}
               disabled={isLoading || specLoading}