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>

PROGRESS.md

@@ -401,9 +401,49 @@ frontend/
 
 ---
 
+## Phase 2: Tree Editor (IN PROGRESS)
+
+### Tree Editor Implementation
+
+**Store**: `frontend/src/store/treeEditorStore.ts`
+- Zustand with immer middleware for immutable updates
+- zundo middleware for undo/redo functionality
+- Node CRUD operations (add, update, delete)
+- nodeMap for O(1) lookups
+- Validation error tracking
+
+**Components Created**:
+
+| Component | Purpose |
+|-----------|---------|
+| `TreeEditorLayout.tsx` | Split-view container (editor 60%, preview 40%) |
+| `TreeMetadataForm.tsx` | Tree name, description, category form |
+| `NodeList.tsx` | List of nodes with add/edit/delete actions |
+| `NodeEditorModal.tsx` | Modal wrapper for node editing |
+| `NodeFormDecision.tsx` | Decision node fields (question, help_text, options) |
+| `NodeFormAction.tsx` | Action node fields (title, description, commands) |
+| `NodeFormResolution.tsx` | Solution node fields (title, steps) |
+| `DynamicArrayField.tsx` | Reusable add/remove array input |
+| `NodePicker.tsx` | Type-grouped dropdown for selecting next_node_id |
+| `TreePreviewPanel.tsx` | Visual tree preview with SharedLinksMap |
+| `TreePreviewNode.tsx` | Node cards with solution indicators |
+
+**Routes Added**:
+- `/trees/new` - Create new tree
+- `/trees/:id/edit` - Edit existing tree
+
+**Key Features**:
+- Form-based editing with live preview
+- NodePicker groups nodes by type (Decision/Action/Solution)
+- Solution connection indicators (green checkmark badges)
+- Shared node detection (shows when multiple nodes link to same target)
+- Modal with scrollable content, fixed header/footer
+
+---
+
 ## What's Next
 
-### Phase 1b: Pre-built Trees (COMPLETE - Hybrid Approach)
+### Phase 1b: Pre-built Trees (Partial)
 
 **Seed Data Script**: `backend/scripts/seed_data.py`
 
@@ -414,16 +454,10 @@ frontend/
 4. 🔲 Citrix VDA Registration - Not started
 5. 🔲 AD Replication Issues - Not started
 
-**Run Seed Script**:
-```bash
-cd backend
-python -m scripts.seed_data
-```
-
 ### Remaining Work
 
-1. **Testing**: End-to-end testing of full workflow
-2. **Polish**: UI refinements, error handling improvements
+1. **Tree Editor Polish**: Validation, required fields, orphan detection
+2. **User Preferences**: Dark mode, export format defaults
 3. **More Trees**: Add remaining 4 trees from `TS-EXAMPLES.md`
 4. **Deployment**: Set up CI/CD pipeline and deploy to Render/Railway
 
@@ -444,15 +478,15 @@ python -m scripts.seed_data
 ## Notes for Next Session
 
 - ✅ Backend **fully tested** - all 18 endpoints working correctly
-- ✅ **Integration tests** - 29 tests with full coverage (all passing)
-- ✅ **Seed script created** with Password Reset tree (full implementation)
+- ✅ **Integration tests** - 40+ tests with full coverage (all passing)
 - ✅ **Frontend COMPLETE** - Full React app with all core pages
+- ✅ **Tree Editor IMPLEMENTED** - Form-based editing with visual preview
 - ✅ **Full workflow tested** - Register → Login → Browse → Navigate → Complete → Export all working
 - 📝 **Single-user focus** for MVP (team features are in schema but low priority)
 
 ### Recommended Next Steps
 
-1. **Polish UI**: Add loading states, better error messages, keyboard shortcuts
-2. **Add more trees**: Implement remaining 4 trees from `TS-EXAMPLES.md`
-3. **Deploy**: Set up CI/CD pipeline and deploy to Render/Railway
-4. **Mobile responsiveness**: Optimize for tablet/mobile use
+1. **Tree Editor Validation**: Required fields, orphan node detection, save validation
+2. **User Preferences**: Dark mode toggle, export format defaults
+3. **Add more trees**: Implement remaining 4 trees from `TS-EXAMPLES.md`
+4. **Deploy**: Set up CI/CD pipeline and deploy to Render/Railway