feat(design): the field family, the dropdown trigger, native controls, the no-raw-input lint rule (E28 S3c)

- ui/Input, Textarea, InnerInput + fieldClass (A4): the >= 3:1 edge, a 2px accent
  focus edge, the danger edge for invalid, md/sm/xs/heading rungs, 1rem and 44 on touch
- ui/SelectTrigger (A5): SortControl, FilterSelect, the view switcher and the date
  filter on one trigger, a pill in a toolbar, r8 in a form
- ui/NativeControls (A6): Checkbox, CheckRow, Slider, ColorInput
- every raw input swept (~100 sites); inputCls retired; local/input-primitive
- useReturnFocus: an in-place editor hands the focus back to its trigger on
  Enter/Escape (the playlist and Plex title renames, the priority number);
  the Plex playlist rename gains Escape and an accessible name
- back to top: a round 48 FAB (owner decision); DESIGN.md A2 and the log

frontend/src/components/plexPlayerControls.tsx

@@ -2,6 +2,7 @@ import { type ReactNode } from "react";
 import { useTranslation } from "react-i18next";
 import { RotateCcw } from "lucide-react";
 import { IconButton } from "./ui/IconButton";
+import { Slider as Range, Checkbox } from "./ui/NativeControls";
 
 // ±10s skip glyph: an outline circular arrow with a "10" in the centre — the YouTube/Plex-native
 // muscle-memory shape. Deliberately distinct from the episode-level SkipBack/SkipForward (double
@@ -93,15 +94,7 @@ export function Slider({
           )}
         </span>
       </div>
-      <input
-        type="range"
-        min={min}
-        max={max}
-        step={step}
-        value={value}
-        onChange={(e) => onChange(Number(e.target.value))}
-        className="w-full accent-accent"
-      />
+      <Range min={min} max={max} step={step} value={value} onChange={(v) => onChange(v)} />
     </div>
   );
 }
@@ -117,12 +110,7 @@ export function Toggle({
   return (
     <label className="flex cursor-pointer items-center justify-between px-1 py-1.5">
       <span className="text-[0.75rem] text-white/80">{label}</span>
-      <input
-        type="checkbox"
-        checked={checked}
-        onChange={(e) => onChange(e.target.checked)}
-        className="h-4 w-4 accent-accent"
-      />
+      <Checkbox checked={checked} onChange={onChange} />
     </label>
   );
 }