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/ChatThread.tsx

@@ -13,6 +13,7 @@ import { notifyActionError } from "../lib/actionErrors";
 import { partnerPub, POLL_MS, refreshPartnerPub, useKeyState } from "../lib/messaging";
 import * as e2ee from "../lib/e2ee";
 import KeyGate from "./KeyGate";
+import { Textarea } from "./ui/Input";
 
 // The message list + composer for one conversation, shared by the full Messages page and the
 // floating dock window. Handles client-side decryption and encrypt-on-send; the surrounding
@@ -210,7 +211,8 @@ export default function ChatThread({
         </div>
       ) : (
         <div className="flex items-end gap-2 p-2 border-t border-border">
-          <textarea
+          <Textarea
+            className="flex-1 resize-none max-h-28"
             value={draft}
             onChange={(e) => setDraft(e.target.value)}
             onKeyDown={(e) => {
@@ -221,7 +223,6 @@ export default function ChatThread({
             }}
             rows={1}
             placeholder={t("messages.writePlaceholder")}
-            className="flex-1 resize-none max-h-28 bg-surface border border-border rounded-xl px-3 py-2 text-sm focus:outline-hidden focus:ring-2 focus:ring-accent/40"
           />
           <IconButton
             label={t("messages.send")}