feat(server-mode): spend quota per user — no new session, prompts refused once used up

An admin sets a default spend quota on the Users page and overrides it per
user (Edit user → Spend quota: default / no limit / their own), in dollars
per local day or per sliding 5 hours. Spend is the users page's own
hourlyTokenRows + calculateCost over the sessions a user owns.

Over the quota, until it opens again:
- spawnRun refuses every start/resume/home prompt with EQUOTA (429);
- a minute sweep writes each pane's AGENTHUB_QUOTA_FILE (host: data dir,
  member: handoff dir via write-as) and hook-handler.js exits 2 on
  UserPromptSubmit from that file alone (Claude Code, Codex with trusted
  hooks) — fail-open, never asks the dashboard, never for Antigravity;
- a member's omp on the shared login loses its gateway key (clientsFor);
- panes no hook can stop (Antigravity, Cursor, Codex without trusted
  hooks, omp on its own login) are ended.

GET /api/me/quota feeds a "Quota N%" chip in the status bar.
New: server/lib/user-quota.js, user_quotas table, PUT /api/users/quota-default,
PATCH /api/users/:id {quota}, docs in SERVER-MODE.md § Spend quotas.

client/src/pages/Users.tsx

@@ -17,7 +17,9 @@
  * an admin — add a user, and ONE Edit per row (`UserEditDialog`: profile,
  * role, active/disabled, password, owned workspaces, sign out everywhere, sent
  * as one change), and the Claude/Codex account pool every user's sessions run
- * on (`AccountPoolCard`).
+ * on (`AccountPoolCard`). Each row's spend shows its spend quota (spent of the
+ * limit, red once used up) and the default quota sits in its own card
+ * (`UserQuota.tsx`); a user's own quota is part of Edit.
  * Every change asks for the admin's OWN password again (the
  * server refuses without it); an analyst only reads. A row shows the display
  * name and email under the username when set, and "New password due" while
@@ -61,6 +63,7 @@ import {
   type AuthUser,
   type MemberTmuxRow,
   type ServerUserUsage,
+  type UserQuota,
   type UserStorage,
 } from "../lib/api";
 import { fmt, fmtCost, formatBytes, formatDateTime } from "../lib/format";
@@ -74,6 +77,7 @@ import { ROLE_BADGE, UserEditDialog } from "../components/users/UserEditDialog";
 import { AccountPoolCard } from "../components/users/AccountPoolCard";
 import { UserDetail } from "../components/users/UserDetail";
 import { UserAvatar } from "../components/users/UserAvatar";
+import { QuotaDefaultCard, QuotaSummary } from "../components/users/UserQuota";
 import {
   MemberTmuxBar,
   TmuxCell,
@@ -104,6 +108,8 @@ export function Users({
   const isAdmin = me?.role === "admin";
 
   const [users, setUsers] = useState<ServerUserUsage[] | null>(null);
+  // The default spend quota (`undefined` until loaded or from an older server).
+  const [quotaDefault, setQuotaDefault] = useState<UserQuota | null | undefined>(undefined);
   const [audit, setAudit] = useState<AuditEntry[] | null>(null);
   const [error, setError] = useState<string | null>(null);
   const [adding, setAdding] = useState(false);
@@ -151,6 +157,7 @@ export function Users({
           .list()
           .then((r) => {
             setUsers(r.users);
+            setQuotaDefault(r.quotaDefault);
             setError(null);
           })
           .catch((e: Error) => setError(e.message)),
@@ -406,6 +413,7 @@ export function Users({
                           month: fmtCost(u.last30d.cost),
                         })}
                       </div>
+                      <QuotaSummary quota={u.quota} />
                     </td>
                     <StorageCell storage={home} measuring={measuring} disk={homesDisk} />
                     {showTmux && (
@@ -487,6 +495,17 @@ export function Users({
           );
         })()}
 
+      {quotaDefault !== undefined && (
+        <QuotaDefaultCard
+          quotaDefault={quotaDefault}
+          isAdmin={isAdmin}
+          onSaved={(message) => {
+            toast.success(message);
+            void load();
+          }}
+        />
+      )}
+
       <AccountPoolCard isAdmin={isAdmin} />
 
       {children}
@@ -559,6 +578,7 @@ export function Users({
       {editing && (
         <UserEditDialog
           user={editing}
+          quotaDefault={quotaDefault ?? null}
           self={editing.id === me.id}
           users={users ?? []}
           onClose={() => setEditing(null)}