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/Messages.tsx

@@ -15,11 +15,11 @@ import { openChat } from "../lib/chatDock";
 import * as e2ee from "../lib/e2ee";
 import Avatar from "./ui/Avatar";
 import KeyGate from "./KeyGate";
-import { inputCls } from "./ui/form";
 import ChatThread from "./ChatThread";
 import NavGrid from "./ui/NavGrid";
 import { navItemAttrs } from "../lib/listNav";
 import { Pressable } from "./ui/Pressable";
+import { Input } from "./ui/Input";
 
 type View =
   | "list"
@@ -235,11 +235,11 @@ function Directory({ onPick, onBack }: { onPick: (u: MessageUser) => void; onBac
         </IconButton>
         <div className="text-xs uppercase tracking-wide text-muted">{t("messages.newTitle")}</div>
       </div>
-      <input
+      <Input
+        className="w-full"
         value={filter}
         onChange={(e) => setFilter(e.target.value)}
         placeholder={t("messages.searchPeople")}
-        className={inputCls}
       />
       {q.isError && !q.data ? (
         <StateMessage tone="error" onRetry={() => q.refetch()}>