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/ui/PriorityStepper.dom.test.tsx

@@ -22,6 +22,20 @@ const lower = () => screen.getByRole("button", { name: "common.priority.lower" }
 const valueBtn = () => screen.getByRole("button", { name: "common.priority.edit" });
 
 describe("PriorityStepper", () => {
+  it("hands the focus back to the value after Enter or Escape, not to <body>", () => {
+    const onSet = vi.fn();
+    render(
+      <PriorityStepper hint="what it orders" priority={3} onPriority={vi.fn()} onSet={onSet} />,
+    );
+    for (const key of ["Escape", "Enter"]) {
+      fireEvent.click(valueBtn());
+      const field = screen.getByRole("spinbutton");
+      field.focus();
+      fireEvent.keyDown(field, { key });
+      expect(document.activeElement).toBe(valueBtn());
+    }
+  });
+
   it("shows the current priority and both step buttons", () => {
     render(
       <PriorityStepper hint="what it orders" priority={12} onPriority={vi.fn()} onSet={vi.fn()} />,