fix: unbroken divider between sidebar and feed

The title bar was one band across the top of the window, so the
sidebar's right border only began below it and the pane read as
detached from the top of the window.

Each pane now reserves its own strip for the traffic lights instead.
The border runs from the very top, and because both insets are the same
height the sidebar header and the top bar share a baseline, so their
bottom borders form one continuous line across the window. Both strips
stay draggable, and the inset collapses in window fullscreen where
there are no traffic lights to clear.

src/App.tsx

@@ -214,19 +214,14 @@ export default function App() {
     return "Nothing matches this filter.";
   };
 
+  // Each pane reserves its own strip for the traffic lights instead of one
+  // band across the top, so the sidebar's right border runs unbroken from the
+  // very top of the window. In macOS window fullscreen there are no traffic
+  // lights, so the inset collapses.
+  const titleBarInset = !windowFullscreen;
+
   return (
     <div className="flex h-screen flex-col">
-      {/* The webview paints the title bar itself. It sits directly above the
-          sidebar and top bar, so it takes the panel colour, not the page's.
-          In macOS window fullscreen the traffic lights are gone, so the strip
-          would just be a blank bar — it collapses instead. */}
-      {!windowFullscreen && (
-        <div
-          data-tauri-drag-region
-          className="h-9 shrink-0 bg-white dark:bg-slate-900"
-        />
-      )}
-
       <div className="relative flex min-h-0 flex-1 flex-col lg:flex-row">
         {/* With the sidebar hidden, a thin strip along the left edge brings it
             back on hover. */}
@@ -251,6 +246,7 @@ export default function App() {
               totalVideos={totals.videos}
               totalDownloaded={totals.downloaded}
               onHide={() => { setSidebarHidden(true); setSidebarPeek(false); }}
+              titleBarInset={titleBarInset}
             />
           </div>
         )}
@@ -264,6 +260,7 @@ export default function App() {
             totalVideos={totals.videos}
             totalDownloaded={totals.downloaded}
             onHide={() => setSidebarHidden(true)}
+            titleBarInset={titleBarInset}
           />
         )}
 
@@ -279,6 +276,7 @@ export default function App() {
           view={view} onView={setView}
           sidebarHidden={sidebarHidden}
           onShowSidebar={() => { setSidebarHidden(false); setSidebarPeek(false); }}
+          titleBarInset={titleBarInset}
         />
 
         {!online && (