feat(FN-670): add mandatory build verification before merge

- Add report_build_failure tool to merger agent for explicit build failure signaling
- Run buildCommand before finalizing merge, abort if build fails with git reset --merge
- Treat build failures as fatal errors (no retry) and keep task in in-review
- Add build verification instruction to executor system prompt
- Update executor to use steeringComments field for mid-execution guidance

packages/dashboard/app/styles.css

@@ -4904,6 +4904,7 @@ body {
 }
 
 .list-cell-title {
+  width: 100%;
   overflow: hidden;
   text-overflow: ellipsis;
   white-space: nowrap;
@@ -5163,6 +5164,7 @@ body {
   }
 
   .list-cell-title {
+    width: 100%;
     overflow: hidden;
     text-overflow: ellipsis;
     white-space: nowrap;