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/WatchPage.tsx

@@ -6,6 +6,7 @@ import { formatBytes } from "../lib/format";
 import { exposeVideoToBackgroundPlay } from "../lib/browserBackgroundPlay";
 import { LS, readJSON, writeJSON } from "../lib/storage";
 import { send } from "../lib/http";
+import { Input } from "./ui/Input";
 
 // Standalone, login-free video page for a shared /watch/<token> link. Rendered OUTSIDE the app
 // tree (no auth, no providers) — like the /privacy and /terms pages. Uses plain fetch and a tiny
@@ -268,7 +269,8 @@ export default function WatchPage() {
               <div className="flex items-center gap-2 font-medium mb-4">
                 <Lock className="w-4 h-4 text-accent" /> {T.passwordTitle}
               </div>
-              <input
+              <Input
+                className="w-full"
                 type="password"
                 value={password}
                 autoFocus
@@ -276,7 +278,6 @@ export default function WatchPage() {
                 onKeyDown={(e) => e.key === "Enter" && password && unlock()}
                 placeholder={T.passwordPlaceholder}
                 aria-describedby={error ? errorId : undefined}
-                className="w-full rounded-lg bg-surface border border-border px-3 py-2 text-sm outline-hidden focus:ring-2 focus:ring-accent/40"
               />
               {/* Announced: focus stays in the input, so a silent message reads as a submit that did nothing. */}
               {error && (