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/PlexSidebar.tsx

@@ -21,6 +21,7 @@ import { useSavedViews } from "./savedViewsContext";
 import { usePlex, usePlexActions } from "./plexContext";
 import { useMe } from "../lib/useMe";
 import { DismissibleChip } from "./ui/Chip";
+import { Input } from "./ui/Input";
 
 // The Plex module's left filter column — now the shared floating SidePanel with its filter groups
 // as reorderable "islands" (same system as the feed rail). Movie libraries get the full metadata
@@ -519,7 +520,9 @@ function NumberInput({
   onChange: (v: number | null) => void;
 }) {
   return (
-    <input
+    <Input
+      className="w-20 tabular-nums"
+      size="sm"
       type="number"
       inputMode="numeric"
       value={value ?? ""}
@@ -528,7 +531,6 @@ function NumberInput({
         const n = e.target.value === "" ? null : Number(e.target.value);
         onChange(n != null && Number.isFinite(n) ? n : null);
       }}
-      className="w-20 rounded-lg border border-border bg-surface px-2 py-1 text-sm tabular-nums focus:outline-hidden focus:ring-2 focus:ring-accent/40"
     />
   );
 }