chore: mark US-031 as complete and update progress log

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

prd.json

@@ -552,7 +552,7 @@
         "Verify in browser using dev-browser skill"
       ],
       "priority": 31,
-      "passes": false,
+      "passes": true,
       "notes": ""
     },
     {

progress.txt

@@ -447,3 +447,17 @@
   - Escape key listener via `document.addEventListener('keydown', handler)` for menu close
   - NodeMouseHandler and EdgeMouseHandler types from reactflow provide proper typing for context menu callbacks
 ---
+
+## 2026-01-22 - US-031
+- What was implemented: Condition editor modal for adding/editing/removing conditions on edges
+- Files changed:
+  - src/components/editor/ConditionEditor.tsx - new modal component with form for variable name, operator, and value
+  - src/app/editor/[projectId]/FlowchartEditor.tsx - integrated condition editor with double-click and context menu triggers
+- **Learnings for future iterations:**
+  - Use `onEdgeDoubleClick` React Flow callback for double-click on edges
+  - Store condition editor state separately from context menu state (`conditionEditor` vs `contextMenu`)
+  - Use `edge.data.condition` to access condition object on edges
+  - When removing properties from edge data, use `delete` operator instead of destructuring to avoid lint warnings about unused variables
+  - Condition type has operators: '>' | '<' | '==' | '>=' | '<=' | '!='
+  - Preview condition in modal using template string: `${variableName} ${operator} ${value}`
+---