feat(design): C5 recorded, every E28 decision taken

The owner's lean Plex control set with both refinements (Back by position,
a touch double-tap for the 10 s skip) goes into DESIGN.md's Players
chapter and the log. The lab is now the reference only.

frontend/src/design-lab/labKit.tsx

@@ -1,84 +1,13 @@
 import { useSyncExternalStore, type ReactNode } from "react";
 import clsx from "clsx";
 
-// Building blocks of the design lab. A lab page asks the owner ONE question per <Decision>: two or
-// three <Variant>s rendered side by side with the app's real CSS, the recommended one marked and its
-// one-line reason (the rule it rests on) printed under it. Everything is static markup on purpose —
-// what is being decided is the look, and a variant that only exists here must not need app state.
-
-export function Decision({
-  id,
-  code,
-  title,
-  question,
-  now,
-  children,
-}: {
-  id: string;
-  code: string;
-  title: string;
-  question: string;
-  /** What the app does today, measured (the E28 S1 inventory). */
-  now: ReactNode;
-  children: ReactNode;
-}) {
-  return (
-    <section id={id} className="glass rounded-2xl p-5 scroll-mt-20">
-      <header className="mb-4">
-        <div className="flex items-baseline gap-3">
-          <span className="text-xs font-bold tracking-widest text-accent">{code}</span>
-          <h2 className="text-lg font-bold">{title}</h2>
-        </div>
-        <p className="mt-1 text-sm">{question}</p>
-        <p className="mt-1 text-xs text-muted">
-          <span className="font-semibold">Today: </span>
-          {now}
-        </p>
-      </header>
-      <div className="grid gap-4 grid-cols-[repeat(auto-fit,minmax(18rem,1fr))]">{children}</div>
-    </section>
-  );
-}
-
-export function Variant({
-  letter,
-  name,
-  recommended = false,
-  why,
-  children,
-}: {
-  letter: string;
-  name: string;
-  recommended?: boolean;
-  why: string;
-  children: ReactNode;
-}) {
-  return (
-    <article
-      className={clsx(
-        "glass-card rounded-xl p-4 flex flex-col gap-3 border",
-        recommended ? "border-accent" : "border-transparent",
-      )}
-    >
-      <div className="flex items-center gap-2">
-        <span className="grid h-6 w-6 place-items-center rounded-full bg-card text-xs font-bold">
-          {letter}
-        </span>
-        <h3 className="text-sm font-semibold flex-1">{name}</h3>
-        {recommended && (
-          <span className="rounded-full bg-accent px-2 py-0.5 text-2xs font-bold text-accent-fg">
-            Recommended
-          </span>
-        )}
-      </div>
-      <div className="flex flex-col gap-3">{children}</div>
-      <p className="mt-auto border-t border-border/60 pt-2 text-xs text-muted">{why}</p>
-    </article>
-  );
-}
+// Building blocks of the design lab. Every E28 decision is taken, so the lab is the reference half
+// only: each <Reference> is the chosen rendering with the rule it became. A new design round brings
+// back the side-by-side <Decision>/<Variant> pair (E28 S2 history) for its open questions. Everything
+// is static markup on purpose: a rendering that only exists here must not need app state.
 
 /** A decision already taken: the chosen rendering only, with the rule it became. The lab's
- *  reference half — the living style guide the open decisions sit on top of. */
+ *  reference half — the living style guide. */
 export function Reference({
   id,
   code,