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- Archive superseded plan docs (RALPH_LOOP V2/V3, CANVAS V3, etc.)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

@@ -0,0 +1,67 @@
+/**
+ * ResizeHandle - Visual drag handle for resizable panels
+ * 
+ * A thin vertical bar that can be dragged to resize panels.
+ * Shows visual feedback on hover and during drag.
+ */
+
+import { memo } from 'react';
+
+interface ResizeHandleProps {
+  /** Mouse down handler to start dragging */
+  onMouseDown: (e: React.MouseEvent) => void;
+  /** Double click handler to reset size */
+  onDoubleClick?: () => void;
+  /** Whether panel is currently being dragged */
+  isDragging?: boolean;
+  /** Position of the handle ('left' or 'right' edge of the panel) */
+  position?: 'left' | 'right';
+}
+
+function ResizeHandleComponent({
+  onMouseDown,
+  onDoubleClick,
+  isDragging = false,
+  position = 'right',
+}: ResizeHandleProps) {
+  return (
+    <div
+      className={`
+        absolute top-0 bottom-0 w-1 z-30
+        cursor-col-resize
+        transition-colors duration-150
+        ${position === 'right' ? 'right-0' : 'left-0'}
+        ${isDragging 
+          ? 'bg-primary-500' 
+          : 'bg-transparent hover:bg-primary-500/50'
+        }
+      `}
+      onMouseDown={onMouseDown}
+      onDoubleClick={onDoubleClick}
+      title="Drag to resize, double-click to reset"
+    >
+      {/* Wider hit area for easier grabbing */}
+      <div 
+        className={`
+          absolute top-0 bottom-0 w-3
+          ${position === 'right' ? '-left-1' : '-right-1'}
+        `}
+      />
+      
+      {/* Visual indicator dots (shown on hover via CSS) */}
+      <div className={`
+        absolute top-1/2 -translate-y-1/2
+        ${position === 'right' ? '-left-0.5' : '-right-0.5'}
+        flex flex-col gap-1 opacity-0 hover:opacity-100 transition-opacity
+        ${isDragging ? 'opacity-100' : ''}
+      `}>
+        <div className="w-1 h-1 rounded-full bg-dark-400" />
+        <div className="w-1 h-1 rounded-full bg-dark-400" />
+        <div className="w-1 h-1 rounded-full bg-dark-400" />
+      </div>
+    </div>
+  );
+}
+
+export const ResizeHandle = memo(ResizeHandleComponent);
+export default ResizeHandle;