fix(theme): R10 S1 follow-ups — dedicated info token + restore collapsed hovers

- Add --info/--info-fg (blue; dark #60a5fa / light #2563eb) so info notifications
  stop borrowing --accent, which collided with a status colour in schemes whose
  accent shares its hue (YouTube red = error, Slate orange = warn, Matrix/Forest
  green = success). Toaster info tone accent -> info.
- Restore hover feedback the codemod flattened: 'bg-X ... hover:bg-X' /
  'text-X ... hover:text-X' collapsed to a no-op once both shades mapped to one
  shadeless token. Reuse the house hover:opacity-{80,90} idiom (ConfirmProvider
  danger button, DownloadCenter error link).

frontend/src/components/DownloadCenter.tsx

@@ -253,7 +253,7 @@ function DownloadRow({
           {job.status === "error" ? (
             <button
               onClick={() => onShowError?.(job)}
-              className="text-danger hover:text-danger inline-flex items-center gap-1 truncate"
+              className="text-danger hover:opacity-80 inline-flex items-center gap-1 truncate"
               title={t("downloads.errors.fail.title")}
             >
               · {t(`downloads.errors.fail.cat.${job.error_code || "unknown"}.short`)}