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/AdminUsers.tsx

@@ -44,6 +44,7 @@ import { PageToolbar } from "./ui/PageShell";
 import { useMe } from "../lib/useMe";
 import { notifyActionError, notifyKnownFailure } from "../lib/actionErrors";
 import { Pressable } from "./ui/Pressable";
+import { Input } from "./ui/Input";
 
 // Admin-only user & access management: roles, access requests (the Invite whitelist), and the
 // demo whitelist + reset. Each section is its own tab (persisted across reloads); the Access tab
@@ -687,12 +688,12 @@ function AdminInvites() {
         }}
         className="flex items-center gap-2 mt-3"
       >
-        <input
+        <Input
+          className="flex-1"
           type="email"
           value={newEmail}
           onChange={(e) => setNewEmail(e.target.value)}
           placeholder={t("settings.invites.addPlaceholder")}
-          className="flex-1 min-w-0 bg-surface border border-border rounded-xl px-3 py-2 text-sm focus:outline-hidden focus:ring-2 focus:ring-accent/40"
         />
         <Button
           type="submit"
@@ -861,12 +862,12 @@ function AdminDemo() {
         }}
         className="flex items-center gap-2"
       >
-        <input
+        <Input
+          className="flex-1"
           type="email"
           value={newEmail}
           onChange={(e) => setNewEmail(e.target.value)}
           placeholder={t("settings.demo.addPlaceholder")}
-          className="flex-1 min-w-0 bg-surface border border-border rounded-xl px-3 py-2 text-sm focus:outline-hidden focus:ring-2 focus:ring-accent/40"
         />
         <Button variant="glass" size="md" className="shrink-0" type="submit">
           <UserPlus className="w-4 h-4" /> {t("settings.demo.add")}