css: stack action buttons full-width on mobile (fix squished Run Research)

After the columns stacked, the three action buttons still shared one
254px row as equal flex:1 thirds — too narrow for the two-word "Run
Research" label, which wrapped and, with the pill radius, rendered as a
circle with overflowing text. On <=900px stack the buttons full-width
with nowrap labels and a moderate 12px radius.

app.py

@@ -1211,6 +1211,21 @@ footer { display: none !important; }
     max-width: 100% !important;
     flex: 1 1 auto !important;
   }
+  /* Action buttons (Run Research / Stop / Clear): three equal flex:1 columns
+     don't leave room for the two-word "Run Research" label on a phone, so it
+     squished into a circle with overflowing text. Stack them full-width. */
+  .action-row {
+    flex-wrap: wrap !important;
+    gap: 8px !important;
+  }
+  .action-row > * {
+    flex: 1 1 100% !important;
+    min-width: 100% !important;
+  }
+  .action-row button {
+    white-space: nowrap !important;
+    border-radius: 12px !important;
+  }
 }
 """