feat(design): every button on its family, the chip primitive, the lint rule (E28 S3b2)

The second half of the button sweep: the remaining hand-rolled buttons in
feature components, the design lab and the components/ui composites now
stand on Button, IconButton, Pressable, Chip or DragHandle.

- Chip + DismissibleChip (filter / token / tag / suggest / ghost, 24px
  floor, 44 on touch) replace five chip geometries; FilterChipGroup
  renders Chips; overflow lanes measure a mirror painted by chipClass.
- The Plex control row is IconButton's player rung (36, 20px glyph,
  round, overlay; 44 on touch); the YT modal bar is on the sm rung with
  pressed cycle toggles and names that survive a folded label.
- New variants: IconButton ghost-accent, danger-soft; Button warn on a
  new state-warn utility. The .btn-{tone} recipes and btnCls are gone.
- Fixed on the way: membership rows (collection editor, Plex playlist
  add) announce checked/mixed; a one-letter tag chip was 21px wide;
  descriptionLinks moved out of lib/ (it renders components).
- local/button-primitive: a raw <button>/<FocusSafeButton> outside the
  control-primitive files is a lint error (contract-tested, seen red).

frontend/src/components/downloadAdmin.tsx

@@ -11,6 +11,8 @@ import { inputCls } from "./ui/form";
 import { Button } from "./ui/Button";
 import { StatusPill } from "./downloadRow";
 import { jobTitle } from "./downloadTitle";
+import { IconButton } from "./ui/IconButton";
+import { Pressable } from "./ui/Pressable";
 
 // The admin "System" tab — storage overview, per-user footprint, quota editor, and the global job
 // list. Split out of DownloadCenter (self-contained, admin-only surface).
@@ -165,18 +167,19 @@ function QuotaUserPicker({ onPick }: { onPick: (u: { id: number; email: string }
       {open && filtered.length > 0 && (
         <div className="absolute z-base mt-1 w-full rounded-lg glass-menu overflow-hidden">
           {filtered.map((u) => (
-            <button
+            <Pressable
               key={u.id}
+              layer
               onClick={() => {
                 onPick({ id: u.id, email: u.email });
                 setQ("");
                 setOpen(false);
               }}
-              className="w-full text-left px-3 py-2 text-sm hover:bg-surface transition flex flex-col"
+              className="w-full px-3 py-2 text-sm flex flex-col"
             >
               <span className="truncate">{u.display_name || u.email}</span>
               {u.display_name && <span className="text-xs text-muted truncate">{u.email}</span>}
-            </button>
+            </Pressable>
           ))}
         </div>
       )}
@@ -225,13 +228,12 @@ export function AdminSystem() {
               >
                 <span className="flex-1 truncate">{u.email}</span>
                 <span className="text-muted">{formatBytes(u.footprint_bytes)}</span>
-                <button
+                <IconButton
                   onClick={() => setQuotaFor({ id: u.user_id, email: u.email ?? "" })}
-                  className="p-1 rounded-sm hover:bg-surface text-muted hover:text-fg"
-                  title={t("downloads.admin.editQuota")}
+                  label={t("downloads.admin.editQuota")}
                 >
-                  <Settings2 className="w-4 h-4" />
-                </button>
+                  <Settings2 />
+                </IconButton>
               </div>
             ))}
             {s.per_user.length === 0 && (