feat(gui): Implement Visual DAG with imgui_node_editor

- Add node editor context and config in App.__init__
- Replace tree-based DAG with imgui_node_editor visualization
- Add selection detection for interactive ticket editing
- Add edit panel for selected ticket (view status, target, deps, mark complete, delete)
- Add ui_selected_ticket_id state variable

conductor/tracks.md

@@ -23,7 +23,7 @@ This file tracks all major tracks for the project. Each track has its own detail
 2. [x] **Track: Deep AST-Driven Context Pruning (RAG for Code)**
    *Link: [./tracks/deep_ast_context_pruning_20260306/](./tracks/deep_ast_context_pruning_20260306/)*
 
-3. [ ] **Track: Visual DAG & Interactive Ticket Editing**
+3. [~] **Track: Visual DAG & Interactive Ticket Editing**
    *Link: [./tracks/visual_dag_ticket_editing_20260306/](./tracks/visual_dag_ticket_editing_20260306/)*
 
 4. [ ] **Track: Advanced Tier 4 QA Auto-Patching**