fix: the collapsed strip ends on the active tab's underline

The underline hangs 2.5px below its tab, onto the band. Collapsed there is no
band to hang onto, so it landed on the ribbon's bottom border with 1px of chrome
under it against 5.5px above. The strip lends it the room while it is alone.

src/lib/components/ribbon/Ribbon.svelte

@@ -142,7 +142,7 @@
 </script>
 
 <div class="ribbon">
-  <div class="ribbon-tabs">
+  <div class="ribbon-tabs" class:strip-only={collapsed}>
     <div class="file-tab-wrap" use:clickOutside={'file'}>
       <button
         class="ribbon-tab-file"
@@ -382,6 +382,10 @@
     padding: 3px 10px 0;
   }
 
+  /* The active tab's underline hangs below its box, onto the band. Collapsed there
+     is no band, so the strip lends it the room instead of the bottom border. */
+  .ribbon-tabs.strip-only { padding-bottom: 5px; }
+
   .ribbon-tab {
     position: relative;
     border: none;