chore: mark US-037 as complete and update progress log

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

prd.json

@@ -658,7 +658,7 @@
         "Typecheck passes"
       ],
       "priority": 37,
-      "passes": false,
+      "passes": true,
       "notes": ""
     },
     {

progress.txt

@@ -534,3 +534,21 @@
   - Track unsaved changes by comparing current state to initialData using JSON.stringify comparison
   - Show confirmation dialog before import if there are unsaved changes to prevent accidental data loss
 ---
+
+## 2026-01-22 - US-037
+- What was implemented: Export to Ren'Py JSON format functionality
+- Files changed:
+  - src/components/editor/Toolbar.tsx - added 'Export to Ren'Py' button with purple styling
+  - src/app/editor/[projectId]/FlowchartEditor.tsx - implemented Ren'Py export types, conversion functions, and handleExportRenpy callback
+- **Learnings for future iterations:**
+  - Ren'Py export uses typed interfaces for different node types: RenpyDialogueNode, RenpyMenuNode, RenpyVariableNode
+  - Find first node by identifying nodes with no incoming edges (not in any edge's target set)
+  - Use graph traversal (DFS) to organize nodes into labeled sections based on flow
+  - Choice nodes create branching sections - save current section before processing each branch
+  - Track visited nodes to detect cycles and create proper labels for jump references
+  - Labels are generated based on speaker name or incremental counter for uniqueness
+  - Replace node IDs with proper labels in a second pass after traversal completes
+  - Include metadata (projectName, exportedAt) at the top level of the export
+  - Validate JSON output with JSON.parse before download to ensure validity
+  - Use purple color scheme for Ren'Py-specific button to distinguish from generic export
+---