Add structured logging and better error handling

web/static/style.css

@@ -349,6 +349,16 @@ button.block {
   gap: 8px;
 }
 
+.banner {
+  background: var(--warning-soft);
+  color: var(--warning);
+  border-bottom: 1px solid var(--border);
+  padding: 10px 16px;
+  text-align: center;
+  font-size: 0.9rem;
+  font-weight: 600;
+}
+
 .content {
   max-width: 980px;
   margin: 0 auto;