bar: centre the row vertically instead of pinning it to the top

Wrapping the bar row in a vbox to gain the drawer slot left the CenterBox at
its natural height, so it sat at the TOP of the window and the remainder
showed as dead space along the bottom edge. Every valign:Center child then
centred within that short box rather than within the bar, and the whole row
rode high.

The clock was the one element that looked right, because it carried a
margin_top(3) nudging it back down. With the row centring properly that offset
would push it below everything else, so it goes too — the compensation and the
bug are the same change.

src/main.rs

@@ -255,6 +255,14 @@ impl SimpleComponent for App {
 
                 #[name = "center_box"]
                 gtk::CenterBox {
+                    // Fill the bar's height. Without this the CenterBox takes
+                    // only its natural height and sits at the TOP of the vbox,
+                    // leaving the remainder as dead space along the bottom
+                    // edge — so every valign:Center child centred within a
+                    // short box rather than within the bar, and the whole row
+                    // rode high. Regression from wrapping the bar row in a
+                    // vbox to gain the drawer slot.
+                    set_vexpand: true,
                 },
 
                 #[name = "drawer_box"]
@@ -506,7 +514,11 @@ impl SimpleComponent for App {
         clock_box.set_valign(gtk4::Align::Center);
         clock_box.set_vexpand(false);
         // Varela Round's em box sits optically high in the 44px island.
-        clock_box.set_margin_top(3);
+        // No compensating margin: this +3 existed to nudge the clock down
+        // against the mis-centred CenterBox above. With the row now filling
+        // the bar height and centring properly, the same offset would push
+        // the clock 3px BELOW everything else.
+        clock_box.set_margin_top(0);
         for digit in &clock_digits {
             clock_box.append(digit);
         }