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- Archive superseded plan docs (RALPH_LOOP V2/V3, CANVAS V3, etc.)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/palette/NodePalette.tsx

@@ -54,6 +54,9 @@ export interface NodePaletteProps {
 // Constants
 // ============================================================================
 
+/** Singleton node types - only one of each allowed on canvas */
+export const SINGLETON_TYPES: NodeType[] = ['model', 'solver', 'algorithm', 'surrogate'];
+
 export const PALETTE_ITEMS: PaletteItem[] = [
   { 
     type: 'model', 
@@ -61,15 +64,15 @@ export const PALETTE_ITEMS: PaletteItem[] = [
     icon: Box, 
     description: 'NX model file (.prt, .sim)', 
     color: 'text-blue-400',
-    canAdd: false, // Synthetic - derived from spec
+    canAdd: true, // Singleton - only one allowed
   },
   { 
     type: 'solver', 
     label: 'Solver', 
     icon: Cpu, 
-    description: 'Nastran solution type', 
+    description: 'Analysis solver config', 
     color: 'text-violet-400',
-    canAdd: false, // Synthetic - derived from model
+    canAdd: true, // Singleton - only one allowed
   },
   { 
     type: 'designVar', 
@@ -109,7 +112,7 @@ export const PALETTE_ITEMS: PaletteItem[] = [
     icon: BrainCircuit, 
     description: 'Optimization method', 
     color: 'text-indigo-400',
-    canAdd: false, // Synthetic - derived from spec.optimization
+    canAdd: true, // Singleton - only one allowed
   },
   { 
     type: 'surrogate', 
@@ -117,7 +120,7 @@ export const PALETTE_ITEMS: PaletteItem[] = [
     icon: Rocket, 
     description: 'Neural acceleration', 
     color: 'text-pink-400',
-    canAdd: false, // Synthetic - derived from spec.optimization.surrogate
+    canAdd: true, // Singleton - only one allowed
   },
 ];