fix(files): an upload is said once in any order, copy buttons speak, a link list that failed says so

- The queue holds an upload it sees land done while this tab's upload still waits for its answer, so
  the dialog's notice is the only one whichever comes first; another device's upload follows after.
- One `useCopyFeedback` for every Copy beside a value (token, share link, set-password link): Copied
  for a moment, a notice a screen reader hears, a warning when the clipboard refuses; the token
  dialog's two Copy buttons are named by what they copy.
- The share dialog's link list shows loading, and a load error with Retry, never "no links" — and no
  New link beside a list it has not seen.
- The settings texts say that signing out elsewhere or a password change revokes the API tokens.
- DESIGN.md logs the folder-link decisions; the design lab keeps only the chosen renderings of the
  Links, Tokens and Files rounds.

frontend/src/components/useCopyFeedback.ts

@@ -0,0 +1,30 @@
+import { useState } from "react";
+import { useTranslation } from "react-i18next";
+
+import { copyText } from "../lib/clipboard";
+import { notify } from "../lib/notifications";
+
+// How long a Copy button reads "Copied" after it worked.
+const COPIED_MS = 2000;
+
+/** The feedback of a Copy button that sits beside the value it copies (a token, a share link, a
+ *  set-password link), the same at every such button: it reads "Copied" for a moment, and a notice
+ *  says it too — the notices are a live region, so a screen reader hears what a swapped label would
+ *  not tell it. A copy that failed is a warning, not an error: the value is on screen and
+ *  selectable, so it is a convenience that failed, not the action.
+ *
+ *  A feature file, not `ui/`: it speaks the app's notifications (as `copyItems` does). */
+export function useCopyFeedback(): { copied: boolean; copy: (value: string) => Promise<void> } {
+  const { t } = useTranslation();
+  const [copied, setCopied] = useState(false);
+  const copy = async (value: string) => {
+    if (await copyText(value)) {
+      setCopied(true);
+      notify({ level: "success", message: t("common.copy.done") });
+      window.setTimeout(() => setCopied(false), COPIED_MS);
+      return;
+    }
+    notify({ level: "warning", message: t("common.copy.failed") });
+  };
+  return { copied, copy };
+}