fix: address the feature review — accurate copy, reachable controls, real coverage

Round 1 on the feature diff found 15; the substantive ones:

- The delete control VANISHED on any invite whose address had registered, which
  is the ordinary sign-up shape (register writes the User and the pending invite
  together). The guard stays broad — that row is the account's approval gate, and
  orphaning it strands someone who can then neither sign in nor be approved — but
  the control is now a disabled button carrying the reason, on both lists, so an
  admin never sees a row silently missing a button its neighbours have.
- Deleting an entry is not always a revoke: is_allowed falls back to the env
  ALLOWED_EMAILS / ADMIN_EMAILS lists once no row exists, and an ADMIN_EMAILS
  address is force-promoted on its next Google sign-in. The route now reports
  still_allowed_by_env and the UI says so instead of claiming access was removed.
- "Deny keeps the row so they can't immediately re-ask" was simply false —
  upsert_pending_invite reopens a denied row. Corrected everywhere it was stated.
- The Configuration warning reads me.email_configured, which save() did not
  invalidate, so it kept warning about fields the admin had just filled in.
- The read-only variant was an aria-hidden span explained only by a Tooltip that
  the hints toggle can switch off; now a disabled button with title + aria-label.
- The delete error path threw away the 409's reason (the stale-list case) and
  left the stale row on screen.
- The throttle window was spent even when no notice was written, silencing the
  next hour on the path whose job is to stop silent drops.
- email_enabled() opened a second session and decrypted the SMTP password on
  every /api/me poll; it now takes the caller's session.
- welcomeMode.dom.test.ts never rendered the card, so reverting the history
  wiring to useState left it green. A render test now drives the real links and
  fails on that revert (verified).

Plus /api/me flag tests, the registration-shaped pending case, the env-allowlist
case, and a release note that matches what the code does.

frontend/src/components/AdminUsers.tsx

@@ -3,7 +3,7 @@ import { qk } from "../lib/queryKeys";
 import { useTranslation } from "react-i18next";
 import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import { Ban, Check, RotateCcw, Shield, Trash2, UserPlus, X } from "lucide-react";
-import { api, type AdminUserRow, type Invite, type Me } from "../lib/api";
+import { api, HttpError, 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";
@@ -301,11 +301,26 @@ function AdminInvites() {
   };
   const remove = useMutation({
     mutationFn: (id: number) => api.deleteInvite(id),
-    onSuccess: (_d, _id) => {
+    onSuccess: (d) => {
       refresh();
-      notify({ level: "success", message: t("settings.invites.deleted") });
+      // Removing the row is not always a revoke: is_allowed falls back to the env allow-lists, so
+      // for an address on those the person keeps access. Saying "removed" alone would mislead.
+      if (d.still_allowed_by_env)
+        notify({ level: "warning", message: t("settings.invites.deletedStillAllowed") });
+      else notify({ level: "success", message: t("settings.invites.deleted") });
+    },
+    onError: (e) => {
+      // A 409 means the list was stale — someone registered on that address since it loaded. Say
+      // what to do instead of a generic failure, and refetch so the row re-renders as read-only.
+      const conflict = e instanceof HttpError && e.status === 409;
+      notify({
+        level: "error",
+        message: t(
+          conflict ? "settings.invites.deleteHasAccount" : "settings.invites.deleteFailed",
+        ),
+      });
+      if (conflict) refresh();
     },
-    onError: () => notify({ level: "error", message: t("settings.invites.deleteFailed") }),
   });
   const onDelete = async (i: { id: number; email: string }) => {
     const ok = await confirm({
@@ -395,11 +410,15 @@ function AdminInvites() {
                 {/* 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>
+                  <button
+                    type="button"
+                    disabled
+                    title={t("settings.invites.deleteHasAccount")}
+                    aria-label={t("settings.invites.deleteHasAccount")}
+                    className="shrink-0 p-1 text-muted/50 cursor-not-allowed"
+                  >
+                    <Trash2 className="w-3.5 h-3.5" />
+                  </button>
                 ) : (
                   <Tooltip hint={t("settings.invites.deleteHint")}>
                     <button
@@ -591,9 +610,21 @@ 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 && (
+      {/* Deny records a decision and keeps the row; delete forgets the address. Once an account
+          exists for it the row is that account's approval gate, so it is managed from Users & roles
+          instead — shown as a disabled control rather than omitted, or the admin sees a row that is
+          silently missing a button their other rows have. */}
+      {inv.has_account ? (
+        <button
+          type="button"
+          disabled
+          title={t("settings.invites.deleteHasAccount")}
+          aria-label={t("settings.invites.deleteHasAccount")}
+          className="shrink-0 p-1.5 rounded-lg border border-border/50 text-muted/50 cursor-not-allowed"
+        >
+          <Trash2 className="w-4 h-4" />
+        </button>
+      ) : (
         <Tooltip hint={t("settings.invites.deleteHint")}>
           <button
             onClick={onDelete}