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/AddToPlaylist.tsx

@@ -10,6 +10,7 @@ import { playlistName } from "../lib/playlistName";
 import { PopoverItem, PopoverSurface } from "./ui/AnchoredPopover";
 import { useAnchoredPopover } from "./ui/anchoredPopoverHooks";
 import { IconButton } from "./ui/IconButton";
+import { Input } from "./ui/Input";
 
 // A small anchored menu for toggling a video's membership in the user's playlists, with inline
 // "new playlist" creation. Same shape as the channel tag editor (R8 S1's pilot): radio-style
@@ -154,7 +155,9 @@ export default function AddToPlaylist({
           </div>
           <div className="flex items-center gap-1.5 border-t border-border mt-1.5 pt-1.5">
             <Plus className="w-3.5 h-3.5 text-muted shrink-0" />
-            <input
+            <Input
+              className="flex-1"
+              size="sm"
               value={newName}
               onChange={(e) => setNewName(e.target.value)}
               onKeyDown={(e) => {
@@ -168,7 +171,6 @@ export default function AddToPlaylist({
                 }
               }}
               placeholder={t("playlists.newPlaylist")}
-              className="flex-1 min-w-0 bg-surface border border-border rounded-md px-2 py-1 text-xs focus:outline-hidden focus:ring-2 focus:ring-accent/40"
             />
           </div>
         </div>