feat(design): dialogs open by purpose and keep their commit row pinned (E28 S3f1)

Modal takes a required initialFocus (field / close / action), a field that
loads late takes the focus while it still rests on the close button, and
ModalFooter portals a dialog's commit row under the scrolling body from any
depth. The header and footer fades follow the body's scroll timeline, and the
viewport's interactive-widget=resizes-content keeps the footer above an
on-screen keyboard.

frontend/src/components/DownloadDialog.tsx

@@ -2,7 +2,7 @@ import { lazy, Suspense, useState } from "react";
 import { qk } from "../lib/queryKeys";
 import { useTranslation } from "react-i18next";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
-import Modal from "./ui/Modal";
+import Modal, { ModalFooter } from "./ui/Modal";
 import { Button } from "./ui/Button";
 import { api } from "../lib/api";
 import { invalidateDownloads } from "../lib/downloads";
@@ -63,7 +63,7 @@ export default function DownloadDialog({
   };
 
   return (
-    <Modal title={t("downloads.dialog.title")} onClose={onClose}>
+    <Modal initialFocus="field" title={t("downloads.dialog.title")} onClose={onClose}>
       {title && <p className="text-sm text-muted mb-4 line-clamp-2">{title}</p>}
 
       <span className="block text-sm font-medium mb-1" aria-hidden="true">
@@ -83,20 +83,20 @@ export default function DownloadDialog({
 
       <label className="block text-sm font-medium mb-1">{t("downloads.dialog.nameLabel")}</label>
       <Input
-        className="w-full mb-5"
+        className="w-full"
         value={name}
         onChange={(e) => setName(e.target.value)}
         placeholder={t("downloads.dialog.namePlaceholder")}
       />
 
-      <div className="flex justify-end gap-2">
+      <ModalFooter>
         <Button variant="ghost" size="sm" onClick={onClose}>
           {t("downloads.actions.cancel")}
         </Button>
         <Button variant="primary" size="sm" onClick={submit} disabled={busy || !chosen}>
           {t("downloads.dialog.submit")}
         </Button>
-      </div>
+      </ModalFooter>
 
       {manage && (
         <Suspense fallback={null}>