Implement Tree Editor with visual preview and documentation updates

Tree Editor Features:
- Zustand store with immer middleware and zundo for undo/redo
- Form-based node editing (Decision, Action, Solution types)
- Visual tree preview with solution connection indicators
- NodePicker with type-grouped dropdown (Decisions/Actions/Solutions)
- SharedLinksMap for detecting nodes with multiple sources
- Modal component with scrollable body, fixed header/footer

New Components:
- TreeEditorLayout, TreeMetadataForm, NodeList, NodeEditorModal
- NodeFormDecision, NodeFormAction, NodeFormResolution
- DynamicArrayField, NodePicker
- TreePreviewPanel, TreePreviewNode

Documentation:
- Updated README.md status to Phase 2
- Added Tree Editor details to CURRENT-STATE.md
- Added modal/Zustand lessons to LESSONS-LEARNED.md
- Updated file structure in CLAUDE-SETUP.md
- Added Tree Editor progress to PROGRESS.md

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/components/tree-editor/NodeFormResolution.tsx

@@ -0,0 +1,129 @@
+import { DynamicArrayField } from './DynamicArrayField'
+import { useTreeEditorStore } from '@/store/treeEditorStore'
+import type { TreeStructure } from '@/types'
+import { cn } from '@/lib/utils'
+
+interface NodeFormResolutionProps {
+  node: TreeStructure
+  onUpdate: (updates: Partial<TreeStructure>) => void
+}
+
+export function NodeFormResolution({ node, onUpdate }: NodeFormResolutionProps) {
+  const { validationErrors } = useTreeEditorStore()
+
+  const titleError = validationErrors.find(
+    e => e.nodeId === node.id && e.field === 'title'
+  )
+
+  const handleAddStep = () => {
+    onUpdate({
+      resolution_steps: [...(node.resolution_steps || []), '']
+    })
+  }
+
+  const handleRemoveStep = (index: number) => {
+    const newSteps = [...(node.resolution_steps || [])]
+    newSteps.splice(index, 1)
+    onUpdate({ resolution_steps: newSteps })
+  }
+
+  const handleUpdateStep = (index: number, value: string) => {
+    const newSteps = [...(node.resolution_steps || [])]
+    newSteps[index] = value
+    onUpdate({ resolution_steps: newSteps })
+  }
+
+  const handleReorderSteps = (fromIndex: number, toIndex: number) => {
+    const newSteps = [...(node.resolution_steps || [])]
+    const [moved] = newSteps.splice(fromIndex, 1)
+    newSteps.splice(toIndex, 0, moved)
+    onUpdate({ resolution_steps: newSteps })
+  }
+
+  return (
+    <div className="space-y-4">
+      {/* Title */}
+      <div>
+        <label className="block text-sm font-medium text-foreground">
+          Title <span className="text-destructive">*</span>
+        </label>
+        <input
+          type="text"
+          value={node.title || ''}
+          onChange={(e) => onUpdate({ title: e.target.value })}
+          placeholder="e.g., VDA Successfully Registered"
+          className={cn(
+            'mt-1 block w-full rounded-md border px-3 py-2 text-sm',
+            'bg-background text-foreground placeholder:text-muted-foreground',
+            'focus:border-primary focus:outline-none focus:ring-1 focus:ring-primary',
+            titleError ? 'border-destructive' : 'border-input'
+          )}
+        />
+        {titleError && (
+          <p className="mt-1 text-xs text-destructive">{titleError.message}</p>
+        )}
+      </div>
+
+      {/* Description */}
+      <div>
+        <label className="block text-sm font-medium text-foreground">
+          Description
+        </label>
+        <textarea
+          value={node.description || ''}
+          onChange={(e) => onUpdate({ description: e.target.value })}
+          placeholder="Summary of the resolution and any follow-up recommendations..."
+          rows={3}
+          className={cn(
+            'mt-1 block w-full rounded-md border border-input px-3 py-2 text-sm',
+            'bg-background text-foreground placeholder:text-muted-foreground',
+            'focus:border-primary focus:outline-none focus:ring-1 focus:ring-primary'
+          )}
+        />
+      </div>
+
+      {/* Resolution Steps */}
+      <div>
+        <label className="block text-sm font-medium text-foreground">
+          Resolution Steps
+        </label>
+        <p className="mb-2 text-xs text-muted-foreground">
+          Step-by-step instructions for resolving the issue
+        </p>
+        <DynamicArrayField
+          items={node.resolution_steps || []}
+          onAdd={handleAddStep}
+          onRemove={handleRemoveStep}
+          onReorder={handleReorderSteps}
+          addLabel="Add Step"
+          renderItem={(step, index) => (
+            <div className="flex items-start gap-2">
+              <span className="mt-2 flex h-5 w-5 shrink-0 items-center justify-center rounded-full bg-primary/10 text-xs font-medium text-primary">
+                {index + 1}
+              </span>
+              <input
+                type="text"
+                value={step}
+                onChange={(e) => handleUpdateStep(index, e.target.value)}
+                placeholder={`Step ${index + 1}`}
+                className={cn(
+                  'block w-full rounded-md border border-input px-3 py-2 text-sm',
+                  'bg-background text-foreground placeholder:text-muted-foreground',
+                  'focus:border-primary focus:outline-none focus:ring-1 focus:ring-primary'
+                )}
+              />
+            </div>
+          )}
+        />
+      </div>
+
+      {/* Note about terminal node */}
+      <div className="rounded-md bg-green-500/10 p-3 text-sm text-green-600 dark:text-green-400">
+        <strong>Note:</strong> Solution nodes are terminal - they end the troubleshooting flow.
+        The session will be marked complete when the user reaches this node.
+      </div>
+    </div>
+  )
+}
+
+export default NodeFormResolution