feat(pool): an admin's switch moves a user's Claude login at once

PUT /api/accounts/pins (and agenthub accounts pin) now writes a pinned
Claude login into the user's home right away (claude-pool.switchHome):
every home's newer pair is copied back first, the member's own login is
never written over, and no pane is restarted — running sessions take the
new pair at their next credentials read. A live home stays on the login it
holds, so unpinning does not flip it back. The Users page calls it
"Switch a user's account" and says what happened.

client/src/components/users/__tests__/AccountPoolCard.test.tsx

@@ -5,8 +5,8 @@
  * admin adds an account only with their own password typed (the token goes
  * in once and is not shown back) — a saved login moved in (the server's own
  * included), or a setup-token — and removes one the same way, and an analyst
- * sees no add or remove control. An admin pins a user to one account and
- * unpins them, each with their own password; the pins show on the accounts.
+ * sees no add or remove control. An admin switches a user to one account and
+ * back to automatic, each with their own password; it shows on the accounts.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
@@ -173,17 +173,20 @@ describe("AccountPoolCard", () => {
       ...POOL,
       pins: { claude: [{ userId: 8, username: "leo", account: "team-1" }], codex: [] },
     });
-    accountPool.pin.mockResolvedValue({ pin: { userId: 7, username: "mia", account: "team-1" } });
+    accountPool.pin.mockResolvedValue({
+      pin: { userId: 7, username: "mia", account: "team-1" },
+      switched: "switched",
+    });
     const user = userEvent.setup();
     render(<AccountPoolCard isAdmin />);
-    expect(await screen.findByText("Pinned: leo")).toBeInTheDocument();
-    await user.click(screen.getByRole("button", { name: /pin a user/i }));
+    expect(await screen.findByText("Used by: leo")).toBeInTheDocument();
+    await user.click(screen.getByRole("button", { name: /switch a user's account/i }));
     const dialog = await screen.findByRole("dialog");
     await waitFor(() => expect(screen.getByRole("option", { name: "mia" })).toBeInTheDocument());
     await user.selectOptions(screen.getByLabelText("User"), "7");
     await user.selectOptions(screen.getByLabelText("Account"), "team-1");
     const confirm = Array.from(dialog.querySelectorAll("button")).find(
-      (b) => b.textContent === "Save pin"
+      (b) => b.textContent === "Switch"
     )!;
     expect(confirm).toBeDisabled();
     await user.type(screen.getByLabelText("Your password"), "boss-pass");
@@ -198,14 +201,17 @@ describe("AccountPoolCard", () => {
       ...POOL,
       pins: { claude: [{ userId: 8, username: "leo", account: "team-1" }], codex: [] },
     });
-    accountPool.pin.mockResolvedValue({ pin: { userId: 8, username: "leo", account: null } });
+    accountPool.pin.mockResolvedValue({
+      pin: { userId: 8, username: "leo", account: null },
+      switched: null,
+    });
     const user = userEvent.setup();
     render(<AccountPoolCard isAdmin />);
-    await user.click(await screen.findByRole("button", { name: "Unpin leo" }));
+    await user.click(await screen.findByRole("button", { name: "Back to automatic for leo" }));
     const dialog = await screen.findByRole("dialog");
     await user.type(screen.getByLabelText("Your password"), "boss-pass");
     await user.click(
-      Array.from(dialog.querySelectorAll("button")).find((b) => b.textContent === "Save pin")!
+      Array.from(dialog.querySelectorAll("button")).find((b) => b.textContent === "Switch")!
     );
     await waitFor(() =>
       expect(accountPool.pin).toHaveBeenCalledWith("claude", 8, null, "boss-pass")