fix(design): an audit of the S3d claims — the float shadow, filter hints, one action size per row (E28 S3d)

- A glass role's shadow is one token (shadow-float); the header search's drop-shadow utility had
  replaced its top highlight, and the debug pill's shadow-lg did the same. The surface-role lint
  rule now refuses a shadow size beside a role.
- Plex: every value that filters carries a hint (genre, certificate, studio had none), and the facts
  panel's year and certificate filter like the header's. filterKeyword -> filterValue.
- Downloads: the row resized its buttons with a [&_button] override that the save link escaped
  (28px beside 32px); the size is the primitive's md rung now.

frontend/src/index.css

@@ -18,6 +18,12 @@
    makes the v4 opacity modifier (bg-accent/40 → color-mix(… var(--accent) 40% …)) pick
    up the active scheme's color. Same pattern as shadcn's v4 theme setup. */
 @theme inline {
+  /* A floating glass surface's shadow: the top specular highlight + the drop. One token so a field that
+     floats (the header search, `shadow-float`) keeps the highlight a menu has — a bare drop-shadow
+     utility would replace both. */
+  --shadow-float:
+    inset 0 1px 0 color-mix(in srgb, #fff calc(var(--glass-inset) - 2%), transparent),
+    0 18px 44px -16px rgba(0, 0, 0, 0.6);
   --color-bg: var(--bg);
   --color-surface: var(--surface);
   --color-card: var(--card);
@@ -499,9 +505,7 @@ body {
       #fff var(--glass-edge),
       color-mix(in srgb, var(--border) 80%, transparent)
     );
-    box-shadow:
-      inset 0 1px 0 color-mix(in srgb, #fff calc(var(--glass-inset) - 2%), transparent),
-      0 18px 44px -16px rgba(0, 0, 0, 0.6);
+    box-shadow: var(--shadow-float);
   }
 
   /* R9: standard interactive-row recipe. The hover tint menu/list rows already use, PLUS the