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- Archive superseded plan docs (RALPH_LOOP V2/V3, CANVAS V3, etc.)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/hooks/useResizablePanel.ts

@@ -0,0 +1,156 @@
+/**
+ * useResizablePanel - Hook for creating resizable panels with persistence
+ * 
+ * Features:
+ * - Drag to resize
+ * - Min/max constraints
+ * - localStorage persistence
+ * - Double-click to reset to default
+ */
+
+import { useState, useCallback, useEffect, useRef } from 'react';
+
+export interface ResizablePanelConfig {
+  /** Unique key for localStorage persistence */
+  storageKey: string;
+  /** Default width in pixels */
+  defaultWidth: number;
+  /** Minimum width in pixels */
+  minWidth: number;
+  /** Maximum width in pixels */
+  maxWidth: number;
+  /** Side of the panel ('left' or 'right') - affects resize direction */
+  side: 'left' | 'right';
+}
+
+export interface ResizablePanelState {
+  /** Current width in pixels */
+  width: number;
+  /** Whether user is currently dragging */
+  isDragging: boolean;
+  /** Start drag handler - attach to resize handle mousedown */
+  startDrag: (e: React.MouseEvent) => void;
+  /** Reset to default width */
+  resetWidth: () => void;
+  /** Set width programmatically */
+  setWidth: (width: number) => void;
+}
+
+const STORAGE_PREFIX = 'atomizer-panel-';
+
+function getStoredWidth(key: string, defaultWidth: number): number {
+  if (typeof window === 'undefined') return defaultWidth;
+  
+  try {
+    const stored = localStorage.getItem(STORAGE_PREFIX + key);
+    if (stored) {
+      const parsed = parseInt(stored, 10);
+      if (!isNaN(parsed)) return parsed;
+    }
+  } catch {
+    // localStorage not available
+  }
+  return defaultWidth;
+}
+
+function storeWidth(key: string, width: number): void {
+  if (typeof window === 'undefined') return;
+  
+  try {
+    localStorage.setItem(STORAGE_PREFIX + key, String(width));
+  } catch {
+    // localStorage not available
+  }
+}
+
+export function useResizablePanel(config: ResizablePanelConfig): ResizablePanelState {
+  const { storageKey, defaultWidth, minWidth, maxWidth, side } = config;
+  
+  // Initialize from localStorage
+  const [width, setWidthState] = useState(() => {
+    const stored = getStoredWidth(storageKey, defaultWidth);
+    return Math.max(minWidth, Math.min(maxWidth, stored));
+  });
+  
+  const [isDragging, setIsDragging] = useState(false);
+  
+  // Track initial position for drag calculation
+  const dragStartRef = useRef<{ x: number; width: number } | null>(null);
+  
+  // Clamp width within bounds
+  const clampWidth = useCallback((w: number) => {
+    return Math.max(minWidth, Math.min(maxWidth, w));
+  }, [minWidth, maxWidth]);
+  
+  // Set width with clamping and persistence
+  const setWidth = useCallback((newWidth: number) => {
+    const clamped = clampWidth(newWidth);
+    setWidthState(clamped);
+    storeWidth(storageKey, clamped);
+  }, [clampWidth, storageKey]);
+  
+  // Reset to default
+  const resetWidth = useCallback(() => {
+    setWidth(defaultWidth);
+  }, [defaultWidth, setWidth]);
+  
+  // Start drag handler
+  const startDrag = useCallback((e: React.MouseEvent) => {
+    e.preventDefault();
+    setIsDragging(true);
+    dragStartRef.current = { x: e.clientX, width };
+  }, [width]);
+  
+  // Handle mouse move during drag
+  useEffect(() => {
+    if (!isDragging) return;
+    
+    const handleMouseMove = (e: MouseEvent) => {
+      if (!dragStartRef.current) return;
+      
+      const delta = e.clientX - dragStartRef.current.x;
+      
+      // For left panels, positive delta increases width
+      // For right panels, negative delta increases width
+      const newWidth = side === 'left'
+        ? dragStartRef.current.width + delta
+        : dragStartRef.current.width - delta;
+      
+      setWidthState(clampWidth(newWidth));
+    };
+    
+    const handleMouseUp = () => {
+      if (dragStartRef.current) {
+        // Persist the final width
+        storeWidth(storageKey, width);
+      }
+      setIsDragging(false);
+      dragStartRef.current = null;
+    };
+    
+    // Add listeners to document for smooth dragging
+    document.addEventListener('mousemove', handleMouseMove);
+    document.addEventListener('mouseup', handleMouseUp);
+    
+    // Change cursor globally during drag
+    document.body.style.cursor = 'col-resize';
+    document.body.style.userSelect = 'none';
+    
+    return () => {
+      document.removeEventListener('mousemove', handleMouseMove);
+      document.removeEventListener('mouseup', handleMouseUp);
+      document.body.style.cursor = '';
+      document.body.style.userSelect = '';
+    };
+  }, [isDragging, side, clampWidth, storageKey, width]);
+  
+  return {
+    width,
+    isDragging,
+    startDrag,
+    resetWidth,
+    setWidth,
+  };
+}
+
+export default useResizablePanel;