feat: move tailscale device discovery and settings into a plugin

Adds plugins/tailscale/ with a devices sidebar tab, admin settings
section, and re-auth dialog. Host Metrics tailscale manager card and
SSH re-auth banner parsing stay in core.

src/ui/tests/plugins/tailscale/AdminTailscaleSection.test.tsx

@@ -0,0 +1,62 @@
+import { describe, expect, it, vi } from "vitest";
+import { render, screen } from "@testing-library/react";
+import userEvent from "@testing-library/user-event";
+import { AdminTailscaleSection } from "../../../../../plugins/tailscale/frontend/AdminTailscaleSection";
+
+vi.mock("react-i18next", () => ({
+  useTranslation: () => ({ t: (key: string) => key }),
+}));
+
+describe("AdminTailscaleSection", () => {
+  it("renders the API key and base URL fields and saves on click", async () => {
+    const user = userEvent.setup();
+    const handleSave = vi.fn();
+    render(
+      <AdminTailscaleSection
+        open
+        onToggle={vi.fn()}
+        tailscaleApiKey="tskey-api-abc"
+        setTailscaleApiKey={vi.fn()}
+        tailscaleApiBaseUrl="https://api.tailscale.com/api/v2"
+        setTailscaleApiBaseUrl={vi.fn()}
+        handleSaveTailscaleApiKey={handleSave}
+      />,
+    );
+
+    expect(
+      (
+        screen.getByPlaceholderText(
+          "tskey-api-... / hskey-api-...",
+        ) as HTMLInputElement
+      ).value,
+    ).toBe("tskey-api-abc");
+    expect(
+      (
+        screen.getByPlaceholderText(
+          "https://api.tailscale.com/api/v2",
+        ) as HTMLInputElement
+      ).value,
+    ).toBe("https://api.tailscale.com/api/v2");
+
+    await user.click(screen.getByText("common.save"));
+    expect(handleSave).toHaveBeenCalledOnce();
+  });
+
+  it("does not render its content when closed", () => {
+    render(
+      <AdminTailscaleSection
+        open={false}
+        onToggle={vi.fn()}
+        tailscaleApiKey=""
+        setTailscaleApiKey={vi.fn()}
+        tailscaleApiBaseUrl=""
+        setTailscaleApiBaseUrl={vi.fn()}
+        handleSaveTailscaleApiKey={vi.fn()}
+      />,
+    );
+
+    expect(
+      screen.queryByPlaceholderText("tskey-api-... / hskey-api-..."),
+    ).toBeNull();
+  });
+});

src/ui/tests/plugins/tailscale/TailscaleDevicesPanel.test.tsx

@@ -0,0 +1,76 @@
+import { describe, expect, it, vi, beforeEach } from "vitest";
+import { render, screen, waitFor } from "@testing-library/react";
+import userEvent from "@testing-library/user-event";
+
+const getTailscaleDevicesMock = vi.hoisted(() => vi.fn());
+
+vi.mock("../../../../../plugins/tailscale/frontend/tailscale-api", () => ({
+  getTailscaleDevices: getTailscaleDevicesMock,
+}));
+
+vi.mock("react-i18next", () => ({
+  useTranslation: () => ({ t: (key: string) => key }),
+}));
+
+import { TailscaleDevicesPanel } from "../../../../../plugins/tailscale/frontend/TailscaleDevicesPanel";
+
+beforeEach(() => {
+  vi.clearAllMocks();
+});
+
+describe("TailscaleDevicesPanel", () => {
+  it("shows the no-api-key message when hasApiKey is false", async () => {
+    getTailscaleDevicesMock.mockResolvedValue({
+      devices: [],
+      hasApiKey: false,
+    });
+
+    render(<TailscaleDevicesPanel onConnect={vi.fn()} />);
+
+    await waitFor(() =>
+      expect(screen.getByText("hosts.tailscaleNoApiKey")).toBeTruthy(),
+    );
+  });
+
+  it("shows the empty-devices message when the tailnet has no devices", async () => {
+    getTailscaleDevicesMock.mockResolvedValue({ devices: [], hasApiKey: true });
+
+    render(<TailscaleDevicesPanel onConnect={vi.fn()} />);
+
+    await waitFor(() =>
+      expect(screen.getByText("hosts.tailscaleNoDevices")).toBeTruthy(),
+    );
+  });
+
+  it("renders devices and connects with an ephemeral tailscale host", async () => {
+    const user = userEvent.setup();
+    getTailscaleDevicesMock.mockResolvedValue({
+      hasApiKey: true,
+      devices: [
+        {
+          id: "d1",
+          name: "box",
+          hostname: "box",
+          addresses: ["100.64.0.1"],
+          os: "linux",
+          lastSeen: "2026-01-01T00:00:00Z",
+        },
+      ],
+    });
+
+    const onConnect = vi.fn();
+    render(<TailscaleDevicesPanel onConnect={onConnect} />);
+
+    await waitFor(() => expect(screen.getByText("box")).toBeTruthy());
+    await user.click(
+      screen.getByText("newUi.sidebar.quickConnect.connectToTerminal"),
+    );
+
+    expect(onConnect).toHaveBeenCalledOnce();
+    const [host, type] = onConnect.mock.calls[0];
+    expect(type).toBe("terminal");
+    expect(host.ip).toBe("100.64.0.1");
+    expect(host.authType).toBe("tailscale");
+    expect(host.username).toBe("root");
+  });
+});

src/ui/tests/plugins/tailscale/tailscale-api.test.ts

@@ -9,7 +9,7 @@ vi.mock("@/main-axios", () => ({
   handleApiError: handleApiErrorMock,
 }));
 
-import { getTailscaleDevices } from "../../api/settings-api";
+import { getTailscaleDevices } from "../../../../../plugins/tailscale/frontend/tailscale-api";
 
 beforeEach(() => {
   vi.clearAllMocks();

src/ui/tests/sidebar/rail-items.test.ts

@@ -57,6 +57,7 @@ describe("RAIL_ITEMS", () => {
       "snippets",
       "macros",
       "fleets",
+      "tailscale",
       "automations",
       "ai",
       "history",