fix(web,adminsite): accessible dialogs, real confirmations, shared async UI

Four correctness/accessibility defects and the destructive-action flow.

- Button: the loading spinner carried xmlns="http://www.w3.instance/2000/svg",
  a find/replace of "org" that landed inside a URL. Button also grows an href
  form, because <Link><Button> nested a button inside an anchor at nineteen
  call sites: invalid markup, two tab stops, and Enter firing only the anchor.

- Fleet status was four meanings carried by hue with the distinction living in
  a title attribute, which touch never shows and screen readers need not
  announce. It now carries a text label and an accessible name, which is the
  one rule the design system states outright.

- Modal had no focus management at all: no trap, no initial focus, no restore,
  no scroll lock, no aria-labelledby. Dialogs nest (a confirm over an edit), so
  a stack decides which panel owns Escape and Tab.

- Seven destructive actions went through window.confirm(). ConfirmDialog
  replaces them and can say what is about to happen; deleting a secret group,
  a shared base step or a workflow now requires typing the name, since those
  have no undo and a wide blast radius. adminsite keeps its own inline idiom
  rather than importing a dialog system it does not have.

Adds Toast, AsyncBoundary/EmptyState/ErrorState/TableSkeleton and
friendlyMessage, replacing per-page loading ternaries and raw
(error as Error).message text. Wired here only where a call site was already
being edited; the remaining pages follow.

adminsite/app/(customer)/users/InvitePanel.tsx

@@ -24,6 +24,7 @@ export function InvitePanel() {
     const [email, setEmail] = useState("");
     const [role, setRole] = useState<AccountRole>("member");
     const [error, setError] = useState<string | null>(null);
+    const [confirming, setConfirming] = useState<string | null>(null);
 
     const users = useQuery({ queryKey: ["account-users"], queryFn: api.accountUsers });
     const refresh = () => qc.invalidateQueries({ queryKey: ["account-users"] });
@@ -46,8 +47,14 @@ export function InvitePanel() {
     });
     const remove = useMutation({
         mutationFn: (id: string) => api.removeAccountUser(id),
-        onSuccess: refresh,
-        onError: fail,
+        onSuccess: () => {
+            setConfirming(null);
+            refresh();
+        },
+        onError: (e) => {
+            setConfirming(null);
+            fail(e);
+        },
     });
 
     if (users.error instanceof NotConnected) return <NotConnectedPanel url={API_BASE} />;
@@ -175,22 +182,46 @@ export function InvitePanel() {
                                             : "Invitation pending"}
                                     </td>
                                     <td className="px-4 py-3 text-right">
-                                        {canManage && !isSelf && (
-                                            <button
-                                                type="button"
-                                                className="text-[0.82rem] font-semibold text-expired underline"
-                                                onClick={() => {
-                                                    if (
-                                                        confirm(
-                                                            `Remove ${u.email}? They lose access to every instance on this account.`,
-                                                        )
-                                                    )
-                                                        remove.mutate(u.user_id);
-                                                }}
-                                            >
-                                                Remove
-                                            </button>
-                                        )}
+                                        {canManage &&
+                                            !isSelf &&
+                                            /*
+                                             * Inline rather than window.confirm(): removing
+                                             * someone here revokes them from every instance
+                                             * on the account, which is more than the word
+                                             * "Remove" beside one row implies, and the
+                                             * browser dialog cannot show the consequence
+                                             * where the eye already is.
+                                             */
+                                            (confirming === u.user_id ? (
+                                                <span className="inline-flex flex-wrap items-center justify-end gap-2">
+                                                    <span className="text-[0.82rem] text-ink-2">
+                                                        Removes access to every instance.
+                                                    </span>
+                                                    <button
+                                                        type="button"
+                                                        className="text-[0.82rem] font-semibold text-expired underline disabled:opacity-50"
+                                                        disabled={remove.isPending}
+                                                        onClick={() => remove.mutate(u.user_id)}
+                                                    >
+                                                        {remove.isPending ? "Removing…" : "Remove"}
+                                                    </button>
+                                                    <button
+                                                        type="button"
+                                                        className="text-[0.82rem] text-ink-2 underline"
+                                                        onClick={() => setConfirming(null)}
+                                                    >
+                                                        Keep
+                                                    </button>
+                                                </span>
+                                            ) : (
+                                                <button
+                                                    type="button"
+                                                    className="text-[0.82rem] font-semibold text-expired underline"
+                                                    onClick={() => setConfirming(u.user_id)}
+                                                >
+                                                    Remove<span className="sr-only"> {u.email}</span>
+                                                </button>
+                                            ))}
                                     </td>
                                 </tr>
                             );