feat(base): add right-side scroll headroom on inline embed grid

Mirror the leftward padding with --embed-grid-pad-right = extendRight,
applied as padding-right on .grid. The user can now pan past the last
column into empty space — same shape as Notion's behavior. Standalone
full-page bases are unaffected (var unset → 0).

apps/client/src/features/base/styles/grid.module.css

@@ -29,6 +29,10 @@
    * scrollable region — the user can pan left into it. Standalone
    * full-page bases never set the var, so it's a no-op there. */
   padding-left: var(--embed-grid-pad-left, 0);
+  /* Symmetric right-side padding lets the user scroll past the last
+   * column into empty space, so wide tables don't end abruptly at
+   * the viewport edge. */
+  padding-right: var(--embed-grid-pad-right, 0);
 }
 
 .headerRow {