chore: Project cleanup and Canvas UX improvements (Phase 7-9)

## Cleanup (v0.5.0)
- Delete 102+ orphaned MCP session temp files
- Remove build artifacts (htmlcov, dist, __pycache__)
- Archive superseded plan docs (RALPH_LOOP V2/V3, CANVAS V3, etc.)
- Move debug/analysis scripts from tests/ to tools/analysis/
- Archive redundant NX journals to archive/nx_journals/
- Archive monolithic PROTOCOL.md to docs/archive/
- Update .gitignore with missing patterns
- Clean old study files (optimization_log_old.txt, run_optimization_old.py)

## Canvas UX (Phases 7-9)
- Phase 7: Resizable panels with localStorage persistence
  - Left sidebar: 200-400px, Right panel: 280-600px
  - New useResizablePanel hook and ResizeHandle component
- Phase 8: Enable all palette items
  - All 8 node types now draggable
  - Singleton logic for model/solver/algorithm/surrogate
- Phase 9: Solver configuration
  - Add SolverEngine type (nxnastran, mscnastran, python, etc.)
  - Add NastranSolutionType (SOL101-SOL200)
  - Engine/solution dropdowns in config panel
  - Python script path support

## Documentation
- Update CHANGELOG.md with recent versions
- Update docs/00_INDEX.md
- Create examples/README.md
- Add docs/plans/CANVAS_UX_IMPROVEMENTS.md

atomizer-dashboard/frontend/src/components/canvas/SpecRenderer.tsx

@@ -49,16 +49,23 @@ import { validateSpec, canRunOptimization } from '../../lib/validation/specValid
 // Drag-Drop Helpers
 // ============================================================================
 
-/** Addable node types via drag-drop */
-const ADDABLE_NODE_TYPES = ['designVar', 'extractor', 'objective', 'constraint'] as const;
+import { SINGLETON_TYPES } from './palette/NodePalette';
+
+/** All node types that can be added via drag-drop */
+const ADDABLE_NODE_TYPES = ['model', 'solver', 'designVar', 'extractor', 'objective', 'constraint', 'algorithm', 'surrogate'] as const;
 type AddableNodeType = typeof ADDABLE_NODE_TYPES[number];
 
 function isAddableNodeType(type: string): type is AddableNodeType {
   return ADDABLE_NODE_TYPES.includes(type as AddableNodeType);
 }
 
+/** Check if a node type is a singleton (only one allowed) */
+function isSingletonType(type: string): boolean {
+  return SINGLETON_TYPES.includes(type as typeof SINGLETON_TYPES[number]);
+}
+
 /** Maps canvas NodeType to spec API type */
-function mapNodeTypeToSpecType(type: AddableNodeType): 'designVar' | 'extractor' | 'objective' | 'constraint' {
+function mapNodeTypeToSpecType(type: AddableNodeType): 'designVar' | 'extractor' | 'objective' | 'constraint' | 'model' | 'solver' | 'algorithm' | 'surrogate' {
   return type;
 }
 
@@ -67,6 +74,22 @@ function getDefaultNodeData(type: AddableNodeType, position: { x: number; y: num
   const timestamp = Date.now();
   
   switch (type) {
+    case 'model':
+      return {
+        name: 'Model',
+        sim: {
+          path: '',
+          solver: 'nastran',
+        },
+        canvas_position: position,
+      };
+    case 'solver':
+      return {
+        name: 'Solver',
+        engine: 'nxnastran',
+        solution_type: 'SOL101',
+        canvas_position: position,
+      };
     case 'designVar':
       return {
         name: `variable_${timestamp}`,
@@ -130,6 +153,23 @@ function getDefaultNodeData(type: AddableNodeType, position: { x: number; y: num
         enabled: true,
         canvas_position: position,
       };
+    case 'algorithm':
+      return {
+        name: 'Algorithm',
+        type: 'TPE',
+        budget: {
+          max_trials: 100,
+        },
+        canvas_position: position,
+      };
+    case 'surrogate':
+      return {
+        name: 'Surrogate',
+        enabled: false,
+        model_type: 'MLP',
+        min_trials: 20,
+        canvas_position: position,
+      };
   }
 }
 
@@ -602,6 +642,18 @@ function SpecRendererInner({
         return;
       }
 
+      // Check if this is a singleton type that already exists
+      if (isSingletonType(type)) {
+        const existingNode = localNodes.find(n => n.type === type);
+        if (existingNode) {
+          // Select the existing node instead of creating a duplicate
+          selectNode(existingNode.id);
+          // Show a toast notification would be nice here
+          console.log(`${type} already exists - selected existing node`);
+          return;
+        }
+      }
+
       // Convert screen position to flow position
       const position = reactFlowInstance.current.screenToFlowPosition({
         x: event.clientX,
@@ -612,8 +664,19 @@ function SpecRendererInner({
       const nodeData = getDefaultNodeData(type, position);
       const specType = mapNodeTypeToSpecType(type);
 
+      // For structural types (model, solver, algorithm, surrogate), these are 
+      // part of the spec structure rather than array items. Handle differently.
+      const structuralTypes = ['model', 'solver', 'algorithm', 'surrogate'];
+      if (structuralTypes.includes(type)) {
+        // These nodes are derived from spec structure - they shouldn't be "added"
+        // They already exist if the spec has that section configured
+        console.log(`${type} is a structural node - configure via spec directly`);
+        setError(`${type} nodes are configured via the spec. Use the config panel to edit.`);
+        return;
+      }
+
       try {
-        const nodeId = await addNode(specType, nodeData);
+        const nodeId = await addNode(specType as 'designVar' | 'extractor' | 'objective' | 'constraint', nodeData);
         // Select the newly created node
         selectNode(nodeId);
       } catch (err) {
@@ -621,7 +684,7 @@ function SpecRendererInner({
         setError(err instanceof Error ? err.message : 'Failed to add node');
       }
     },
-    [editable, addNode, selectNode, setError]
+    [editable, addNode, selectNode, setError, localNodes]
   );
 
   // Loading state