feat: Add panel management, validation, and error handling to canvas

Phase 1 - Panel Management System:
- Create usePanelStore.ts for centralized panel state management
- Add PanelContainer.tsx for draggable floating panels
- Create FloatingIntrospectionPanel.tsx (persistent, doesn't disappear on node click)
- Create ResultsPanel.tsx for trial result details
- Refactor NodeConfigPanelV2 to use panel store for introspection
- Integrate PanelContainer into CanvasView

Phase 2 - Pre-run Validation:
- Create specValidator.ts with comprehensive validation rules
- Add ValidationPanel (enhanced version with error navigation)
- Add Validate button to SpecRenderer with status indicator
- Block run if validation fails
- Check for: design vars, objectives, extractors, bounds, connections

Phase 3 - Error Handling & Recovery:
- Create ErrorPanel.tsx for displaying optimization errors
- Add error classification (nx_crash, solver_fail, extractor_error, etc.)
- Add recovery suggestions based on error type
- Update status endpoint to return error info
- Add _get_study_error_info helper to check error_status.json and DB
- Integrate error detection into status polling

Documentation:
- Add CANVAS_ROBUSTNESS_PLAN.md with full implementation plan

atomizer-dashboard/frontend/src/components/canvas/panels/NodeConfigPanelV2.tsx

@@ -17,8 +17,8 @@ import {
   useSelectedNodeId,
   useSelectedNode,
 } from '../../../hooks/useSpecStore';
+import { usePanelStore } from '../../../hooks/usePanelStore';
 import { FileBrowser } from './FileBrowser';
-import { IntrospectionPanel } from './IntrospectionPanel';
 import {
   DesignVariable,
   Extractor,
@@ -272,7 +272,15 @@ interface SpecConfigProps {
 }
 
 function ModelNodeConfig({ spec }: SpecConfigProps) {
-  const [showIntrospection, setShowIntrospection] = useState(false);
+  const { setIntrospectionData, openPanel } = usePanelStore();
+  
+  const handleOpenIntrospection = () => {
+    // Set up introspection data and open the panel
+    setIntrospectionData({
+      filePath: spec.model.sim?.path || '',
+      studyId: useSpecStore.getState().studyId || undefined,
+    });
+  };
   
   return (
     <>
@@ -300,7 +308,7 @@ function ModelNodeConfig({ spec }: SpecConfigProps) {
 
       {spec.model.sim?.path && (
         <button
-          onClick={() => setShowIntrospection(true)}
+          onClick={handleOpenIntrospection}
           className="w-full flex items-center justify-center gap-2 px-3 py-2.5 bg-primary-500/20
                      hover:bg-primary-500/30 border border-primary-500/30 rounded-lg
                      text-primary-400 text-sm font-medium transition-colors"
@@ -309,16 +317,8 @@ function ModelNodeConfig({ spec }: SpecConfigProps) {
           Introspect Model
         </button>
       )}
-
-      {showIntrospection && spec.model.sim?.path && (
-        <div className="fixed top-20 right-96 z-40">
-          <IntrospectionPanel
-            filePath={spec.model.sim.path}
-            studyId={useSpecStore.getState().studyId || undefined}
-            onClose={() => setShowIntrospection(false)}
-          />
-        </div>
-      )}
+      
+      {/* Note: IntrospectionPanel is now rendered by PanelContainer, not here */}
     </>
   );
 }