fix(grid): add bottom padding to grid panes so the focus ring/border doesn't crowd the last terminal line

Grid-cell panes had 0 bottom padding (single mode fills to the key-bar), so the
last terminal row butted against the cell border and the gold focus ring looked
like it covered the text. Adds 6px bottom clearance in grid mode only.

public/style.css

@@ -357,6 +357,12 @@ body {
   border-radius: var(--radius);
   background: var(--bg);
 }
+/* In a grid cell the pane butts against the cell's border; without a bottom gap
+ * the last terminal row sits under the border/focus ring. Give it clearance
+ * (single mode keeps padding 0 so the terminal fills to the key-bar as before). */
+#term.grid .term-pane {
+  padding-bottom: 6px;
+}
 /* Maximized quadrant fills the whole grid as an ABSOLUTE overlay (taken out of
  * grid flow so the siblings keep their placement — spanning grid tracks instead
  * would shove auto-placed siblings into implicit rows, resizing their live PTYs).