Refactor layout styles for improved responsiveness; add video height constraint on resize

static/css/style.css

@@ -82,17 +82,18 @@ header {
   text-transform: uppercase;
 }
 
-/* Layout: row with golden-ratio split, collapse on small */
+/* Layout: row with split, collapse on small */
 .layout {
   display: flex;
   flex-direction: row;
-  align-items: flex-start;
+  align-items: stretch;
   gap: 20px;
   padding: 20px 24px;
   flex: 1;
   max-width: 100%;
   margin: 0 auto;
   width: 100%;
+  min-height: 0;
 }
 
 /* Region filter bar */
@@ -144,6 +145,7 @@ header {
   flex-direction: column;
   gap: 12px;
   min-width: 0;
+  min-height: 0;
 }
 
 .video-stage {
@@ -154,6 +156,8 @@ header {
   box-shadow: var(--shadow);
   border: 1px solid var(--border);
   width: 100%;
+  flex: 1;
+  min-height: 0;
 }
 .video-stage video {
   width: 100%;