refactor: sweep call sites onto design-system utilities + bug fixes

Replace inline class clusters with the design-system utilities and
tokens established in the prior two commits. No behavior changes
intended beyond two real bug fixes.

Bug fixes:
- SampleList.svelte: 'border-border-subtle bg-background-40' was a
  silent no-op (both classes mis-spelled). Now 'border-subtle
  bg-background/40' applies as intended.
- FontList.svelte: 'h-[44px]' → 'h-11' (44px = 2.75rem = spacing-11,
  no need for arbitrary value).

Sweeps:
- TypographyMenu: popover + floating bar now use surface-popover /
  surface-floating + shadow-popover.
- FontList + FilterGroup: tertiary list buttons use the new
  Button layout="block-list-row" variant; skeleton fills use
  the skeleton-fill utility.
- Footer / BreadcrumbHeader: surface-floating absorbs the
  bg-surface/blur/border cluster. Footer bumped to z-20 with a
  comment explaining the stacking against SidebarContainer (z-40/50).
- FontSampler: surface-card + hover shadow-stamp-card token.
- SliderArea: surface-canvas, flex-center, shadow-floating-panel
  tokens (light + dark variants).
- Sidebar / Header / ButtonGroup / Layout / SidebarContainer:
  bg-surface dark:bg-dark-bg → surface-canvas (8 sites);
  SidebarContainer mobile panel uses shadow-overlay.
- Loader / Thumb: flex items-center justify-center → flex-center;
  Thumb durations → duration-fast.
- ComboControl: trigger uses surface-card-elevated when open,
  popover uses surface-card-elevated, label cluster → text-label-mono,
  flex-center for the trigger interior.
- Slider: shadow-sm → shadow-rest, duration-150 → duration-fast.
- text-secondary → text-subtle across Input, Slider, ComboControl
  (matches the rename in the styles commit).
- Link: reverted earlier surface-floating attempt — Link's original
  bg-surface/80 backdrop-blur pattern was thinner than surface-floating
  (no border, smaller blur), and the Footer was overlaying its own
  border-subtle on top, fighting the utility. Kept the original style.

src/features/AdjustTypography/ui/TypographyMenu/TypographyMenu.svelte

@@ -90,11 +90,8 @@ $effect(() => {
                         align="end"
                         sideOffset={8}
                         class={cn(
-                            'z-50 w-72',
-                            'bg-surface dark:bg-dark-card',
-                            'border border-subtle',
-                            'shadow-[0_20px_40px_-10px_rgba(0,0,0,0.15)]',
-                            'rounded-none p-4',
+                            'z-50 w-72 p-4 rounded-none',
+                            'surface-popover',
                             'data-[state=open]:animate-in data-[state=closed]:animate-out',
                             'data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0',
                             'data-[state=closed]:zoom-out-95 data-[state=open]:zoom-in-95',
@@ -118,7 +115,7 @@ $effect(() => {
                                 {#snippet child({ props })}
                                     <button
                                         {...props}
-                                        class="inline-flex items-center justify-center size-6 rounded-none hover:bg-black/5 dark:hover:bg-white/5 transition-colors"
+                                        class="flex-center size-6 rounded-none hover:bg-black/5 dark:hover:bg-white/5 transition-colors"
                                         aria-label="Close controls"
                                     >
                                         <XIcon class="size-3.5 text-neutral-500" />
@@ -150,10 +147,9 @@ $effect(() => {
             <div
                 class={cn(
                     'flex items-center gap-1 md:gap-2 p-1.5 md:p-2',
-                    'bg-surface/95 dark:bg-dark-bg/95 backdrop-blur-xl',
-                    'border border-subtle',
-                    'shadow-[0_20px_40px_-10px_rgba(0,0,0,0.1)]',
-                    'rounded-none ring-1 ring-black/5 dark:ring-white/5',
+                    'surface-floating bg-surface/95 dark:bg-dark-bg/95 backdrop-blur-xl',
+                    'shadow-popover rounded-none',
+                    'ring-1 ring-black/5 dark:ring-white/5',
                 )}
             >
                 <!-- Header: icon + label -->

src/features/DisplayFont/ui/FontSampler/FontSampler.svelte

@@ -58,12 +58,10 @@ const stats = $derived([
     class="
         group relative
         w-full h-full
-        bg-paper dark:bg-dark-card
-        border border-subtle
+        surface-card
         hover:border-brand dark:hover:border-brand
-        hover:shadow-brand/10
-        hover:shadow-[5px_5px_0px_0px]
-        transition-all duration-200
+        hover:shadow-stamp-card
+        transition-all duration-normal
         overflow-hidden
         flex flex-col
         min-h-60