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/PlaylistsRail.tsx

@@ -25,6 +25,7 @@ import { usePlaylistActions } from "./usePlaylistActions";
 import PlaylistLimitsHint from "./PlaylistLimitsHint";
 import { IconButton } from "./ui/IconButton";
 import { Pressable } from "./ui/Pressable";
+import { Input } from "./ui/Input";
 
 type PlSort = {
   key: "custom" | "name" | "count" | "duration" | "recent";
@@ -276,12 +277,13 @@ export default function PlaylistsRail({
             className="flex items-center gap-1.5"
           >
             <Plus className="w-4 h-4 text-muted shrink-0" />
-            <input
+            <Input
+              className="flex-1"
+              size="sm"
               value={newName}
               onChange={(e) => setNewName(e.target.value)}
               placeholder={t("playlists.newPlaylist")}
               disabled={!canWrite}
-              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 disabled:opacity-50"
             />
           </form>
         </div>
@@ -322,7 +324,9 @@ export default function PlaylistsRail({
                       <img src={pl.cover_thumbnail} alt="" className="w-full h-full object-cover" />
                     )}
                   </div>
-                  <input
+                  <Input
+                    className="flex-1"
+                    size="sm"
                     ref={renameInputRef}
                     value={renameValue}
                     onChange={(e) => setRenameValue(e.target.value)}
@@ -339,7 +343,6 @@ export default function PlaylistsRail({
                       }
                     }}
                     aria-label={t("playlists.rename")}
-                    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>
               ) : (