fix: enable scrollbar on detail panel tab content

The flex chain from detailArea → detailPanel → tabContent lacked
min-height: 0, so flex children never shrank below content height
and overflow-y: auto never triggered. Added min-height: 0 and
flex: 1 to propagate the height constraint correctly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/components/ExecutionDiagram/ExecutionDiagram.module.css

@@ -75,6 +75,8 @@
 .detailArea {
   overflow: hidden;
   min-height: 120px;
+  display: flex;
+  flex-direction: column;
 }
 
 .loadingState {
@@ -109,6 +111,8 @@
   overflow: hidden;
   background: var(--bg-surface, #FFFFFF);
   border-top: 1px solid var(--border, #E4DFD8);
+  flex: 1;
+  min-height: 0;
 }
 
 .processorHeader {
@@ -220,6 +224,7 @@
    ========================================================================== */
 .tabContent {
   flex: 1;
+  min-height: 0;
   overflow-y: auto;
   padding: 10px 14px;
 }