feat(admin): delete a whitelist entry, and stop hiding a broken mail setup

Three operator gaps, all found the same way — a person could not sign up and the
app showed nobody anything.

- DELETE /api/admin/invites/{id} with a delete control on both the pending
  requests and the previously-decided list. Deny keeps the row so the person
  cannot immediately re-ask; delete forgets the address. Refused with 409 while
  a User row exists for it, because is_allowed reads that row and removing it
  would revoke a live user's access with no other sign — the list ships
  has_account so the UI withholds the button instead of offering one that fails.
- Email is fail-soft by design, which had come to mean invisible. _send() now
  records an email_undelivered notification for every admin when a message is
  skipped or rejected, naming the message that was lost, throttled to one an
  hour. /api/me carries email_configured, driving a standing warning on
  Configuration → Email / SMTP and above the access-request list.
- The sign-in card's Create account / Forgot password / Didn't get the email
  views are history entries (useHistorySubview), so Back returns to the previous
  view instead of only moving the address bar.

Also: the per-test rate-limiter reset sweeps every loaded app.* module rather
than a hand-kept list of three — this change added a limiter outside it.

frontend/src/components/AdminUsers.tsx

@@ -7,6 +7,7 @@ import { api, type AdminUserRow, type Invite, type Me } from "../lib/api";
 import { notify } from "../lib/notifications";
 import { ADMIN_USERS_TAB_KEY } from "../lib/adminUsersTab";
 import Tooltip from "./Tooltip";
+import InlineNotice from "./InlineNotice";
 import { Section } from "./ui/form";
 import { LoadingState, StateMessage } from "./QueryState";
 import { useConfirm } from "./ConfirmProvider";
@@ -266,6 +267,7 @@ function AdminInvites() {
   const { t } = useTranslation();
   const qc = useQueryClient();
   const confirm = useConfirm();
+  const me = useMe();
   const invites = useQuery({ queryKey: qk.adminInvites(), queryFn: () => api.adminInvites() });
   const [newEmail, setNewEmail] = useState("");
   const refresh = () => {
@@ -297,6 +299,23 @@ function AdminInvites() {
     });
     if (ok) deny.mutate(i.id);
   };
+  const remove = useMutation({
+    mutationFn: (id: number) => api.deleteInvite(id),
+    onSuccess: (_d, _id) => {
+      refresh();
+      notify({ level: "success", message: t("settings.invites.deleted") });
+    },
+    onError: () => notify({ level: "error", message: t("settings.invites.deleteFailed") }),
+  });
+  const onDelete = async (i: { id: number; email: string }) => {
+    const ok = await confirm({
+      title: t("settings.invites.deleteTitle"),
+      message: t("settings.invites.deleteConfirm", { email: i.email }),
+      confirmLabel: t("settings.invites.delete"),
+      danger: true,
+    });
+    if (ok) remove.mutate(i.id);
+  };
   const add = useMutation({
     mutationFn: (email: string) => api.addInvite(email),
     onSuccess: (_d, email) => {
@@ -313,6 +332,9 @@ function AdminInvites() {
 
   return (
     <Section card title={t("settings.invites.title")}>
+      {!me.email_configured && (
+        <InlineNotice className="mb-3">{t("settings.invites.emailOff")}</InlineNotice>
+      )}
       {invites.isError && !invites.data ? (
         <StateMessage tone="error" onRetry={() => invites.refetch()}>
           {t("common.loadError")}
@@ -329,7 +351,8 @@ function AdminInvites() {
               inv={i}
               onApprove={() => approve.mutate({ id: i.id, email: i.email })}
               onDeny={() => onDeny(i)}
-              busy={approve.isPending || deny.isPending}
+              onDelete={() => onDelete(i)}
+              busy={approve.isPending || deny.isPending || remove.isPending}
             />
           ))}
         </div>
@@ -364,11 +387,31 @@ function AdminInvites() {
           </summary>
           <div className="mt-2 space-y-1 text-xs text-muted">
             {decided.map((i) => (
-              <div key={i.id} className="flex items-center justify-between gap-2">
-                <span className="truncate">{i.email}</span>
+              <div key={i.id} className="flex items-center gap-2">
+                <span className="truncate flex-1">{i.email}</span>
                 <span className={i.status === "approved" ? "text-accent" : "text-danger"}>
                   {i.status}
                 </span>
+                {/* An entry with an account behind it stays read-only: deleting it would revoke that
+                    user's access, since is_allowed reads this row. Delete the user instead. */}
+                {i.has_account ? (
+                  <Tooltip hint={t("settings.invites.deleteHasAccount")}>
+                    <span className="shrink-0 p-1 text-muted/50" aria-hidden>
+                      <Trash2 className="w-3.5 h-3.5" />
+                    </span>
+                  </Tooltip>
+                ) : (
+                  <Tooltip hint={t("settings.invites.deleteHint")}>
+                    <button
+                      onClick={() => onDelete(i)}
+                      disabled={remove.isPending}
+                      className="shrink-0 p-1 rounded-md text-muted hover:text-danger disabled:opacity-50 transition"
+                      aria-label={t("settings.invites.deleteLabel", { email: i.email })}
+                    >
+                      <Trash2 className="w-3.5 h-3.5" />
+                    </button>
+                  </Tooltip>
+                )}
               </div>
             ))}
           </div>
@@ -506,11 +549,13 @@ function InviteRow({
   inv,
   onApprove,
   onDeny,
+  onDelete,
   busy,
 }: {
   inv: Invite;
   onApprove: () => void;
   onDeny: () => void;
+  onDelete: () => void;
   busy: boolean;
 }) {
   const { t } = useTranslation();
@@ -546,6 +591,20 @@ function InviteRow({
           <X className="w-4 h-4" />
         </button>
       </Tooltip>
+      {/* Deny keeps the row (so the person can't immediately re-ask); delete forgets the address
+          entirely. Withheld once an account exists — that would revoke a live user's access. */}
+      {!inv.has_account && (
+        <Tooltip hint={t("settings.invites.deleteHint")}>
+          <button
+            onClick={onDelete}
+            disabled={busy}
+            className="shrink-0 p-1.5 rounded-lg border border-border text-muted hover:text-danger disabled:opacity-50 transition"
+            aria-label={t("settings.invites.deleteLabel", { email: inv.email })}
+          >
+            <Trash2 className="w-4 h-4" />
+          </button>
+        </Tooltip>
+      )}
     </div>
   );
 }