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/plexDetailUi.tsx

@@ -1,4 +1,4 @@
-import { useRef, useState, type ReactNode } from "react";
+import { useRef, useState, type ReactNode, type Ref } from "react";
 import { useTranslation } from "react-i18next";
 import {
   ArrowLeft,
@@ -170,6 +170,7 @@ export function BackBtn({ onBack, label }: { onBack: () => void; label: string }
 }
 
 export function ActionBtn({
+  ref,
   onClick,
   icon: Icon,
   label,
@@ -183,9 +184,11 @@ export function ActionBtn({
   sub?: string;
   primary?: boolean;
   disabled?: boolean;
+  ref?: Ref<HTMLButtonElement>;
 }) {
   return (
     <Button
+      ref={ref}
       variant={primary ? "primary" : "glass"}
       onClick={onClick}
       disabled={disabled}