feat(pool): pin a user to one Claude/Codex pool account

An admin pins a server-mode user to one pool account per tool
(account_pins; PUT /api/accounts/pins with the password step-up and audit,
the Users page's Pin a user, agenthub accounts pin|unpin). The workspace
owner's pin wins over the balancer whenever the pane may use the account;
a pinned login still waits while another pool login holds the home.

client/src/lib/api.ts

@@ -676,9 +676,18 @@ export type CodexPoolAccount = {
   quotaPercent: number | null;
   full: boolean;
 };
+/** A user an admin pinned to one pool account: their new sessions skip the balancer. */
+export type AccountPin = {
+  userId: number;
+  username: string;
+  account: string;
+  pinnedAt?: string;
+};
 export type AccountPool = {
   accounts: PoolAccount[];
   codex: CodexPoolAccount[];
+  /** Per tool; absent from an older server, empty in local mode. */
+  pins?: { claude: AccountPin[]; codex: AccountPin[] };
   blockPercent: number;
 };
 export type PoolTool = "claude" | "codex";
@@ -1052,6 +1061,15 @@ export const api = {
         method: "POST",
         body: JSON.stringify({ ...body, currentPassword }),
       }),
+    /** PUT /api/accounts/pins — admin: pin a user to one account (`null` unpins), password again. */
+    pin: (tool: PoolTool, userId: number, account: string | null, currentPassword: string) =>
+      request<{ pin: { userId: number; username: string; account: string | null } }>(
+        "/accounts/pins",
+        {
+          method: "PUT",
+          body: JSON.stringify({ tool, userId, account, currentPassword }),
+        }
+      ),
     /** DELETE /api/accounts/:name — admin, with their OWN password again. */
     remove: (tool: PoolTool, name: string, currentPassword: string) =>
       request<{ ok: true }>(`/accounts/${encodeURIComponent(name)}`, {