fix(frontend): drop 12px font pin on header icon cards to match reference

The reference theme renders header slider icon cards on the bootstrap
14px body baseline (title .em12 -> 16.8px, desc 14px). A local
.header-slider-card .icon-cover-card { font-size: 12px } override shrank
text to 14.4/12px, making AKSRT cards visibly smaller than the reference.
Remove the pin from base.css and the public bundle; container gutter
restoration stays.

assets/css/frontend/base.css

@@ -104,14 +104,6 @@ main.container,
   box-sizing: border-box;
 }
 
-/* Header multifunc icon cards: pin typography baseline so cards render
- * identically on all pages. .px12-sm is only defined globally in
- * legacy-utilities.css, which is @import'd by the single-post aggregator;
- * vendor CSS pins it at <=640px / .sidebar / .mobile-nav-widget only. */
-.header-slider-card .icon-cover-card {
-  font-size: 12px;
-}
-
 /* Keep the header multifunction search stable across route-specific CSS.
  * Some routes load a later .abs-right utility, while the global input focus
  * ring looks like an extra border against this transparent pill field. */