feat(design): the NavRail primitive with optional short labels, the flat surfaces onto roles (E28 S3d3, B7/B5)

frontend/src/index.css

@@ -563,8 +563,7 @@ body {
      in @layer components, a site's own utility still wins — so a MIGRATED site must DROP its bg/text/
      border-color utilities (else a utility-layer `bg-*` beats the recipe's pressed fill). Add
      data-soft="true" for the subtle tint some surfaces use instead of the solid fill. */
-  .pill,
-  .is-current {
+  .pill {
     color: var(--muted);
     transition:
       color 0.15s ease,
@@ -576,25 +575,18 @@ body {
   /* Resting border colour for the plain pills. NOT applied to a glass-card-resting pill (`.pill.glass-card`),
      whose own border — including its lighter top-edge specular highlight — must survive. Inert unless the
      site also adds a border-width utility. */
-  .pill:not(.glass-card),
-  .is-current {
+  .pill:not(.glass-card) {
     border-color: var(--border);
   }
-  .pill:hover,
-  .is-current:hover {
+  .pill:hover {
     color: var(--fg);
   }
   .pill:hover {
     border-color: color-mix(in srgb, var(--accent) 55%, transparent);
   }
-  .is-current:hover {
-    background-color: var(--card);
-  }
-  /* selected / current — SOLID accent fill (the dominant idiom). The `:not([aria-current="false"])`
-     guard matters: `.is-current` is a shared primitive and a consumer using the common
-     `aria-current={x ? "true" : "false"}` idiom would otherwise paint a NON-current row as current. */
-  .pill[aria-pressed="true"],
-  .is-current[aria-current]:not([aria-current="false"]) {
+  /* selected — SOLID accent fill (the dominant idiom). (The nav rail's "you are here" is ui/NavRail's
+     tint + edge bar since E28 S3d; its old `.is-current` recipe is gone.) */
+  .pill[aria-pressed="true"] {
     background-color: var(--accent);
     color: var(--accent-fg);
     border-color: var(--accent);