chore: mark US-023 as complete and update progress log

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

prd.json

@@ -408,7 +408,7 @@
         "Verify in browser using dev-browser skill"
       ],
       "priority": 23,
-      "passes": false,
+      "passes": true,
       "notes": ""
     },
     {

progress.txt

@@ -351,3 +351,14 @@
   - Each option needs a unique id (string) and label (string) per the ChoiceOption type
   - updateOptionLabel callback pattern: find option by id, map over options array to update matching one
 ---
+
+## 2026-01-21 - US-023
+- What was implemented: Add choice node from toolbar functionality
+- Files changed:
+  - src/app/editor/[projectId]/FlowchartEditor.tsx - implemented handleAddChoice to create new choice nodes at viewport center
+- **Learnings for future iterations:**
+  - handleAddChoice follows same pattern as handleAddDialogue: get viewport center, create node with nanoid, add to state
+  - Choice nodes must be initialized with 2 options (each with unique id via nanoid and empty label)
+  - Node data structure for choice: { prompt: '', options: [{ id, label }, { id, label }] }
+  - React Flow nodes are draggable by default after being added to state
+---