Pair displays at the platform's own /display/setup, with or without modules

Displays are platform-owned, but a screen could only start pairing on a
module's display page: every pairing request named a module, so an
installation with no module that uses displays could not set one up.

- /display/setup is the platform's own display page, served whenever
  the deployment has device support, whatever is installed. It pairs a
  platform display with no module. Once paired, it opens the module it
  is set to show; with none set, it shows its name and waits, rechecking
  so it stays alive and notices revocation. "setup" is now a reserved
  module id.
- Migration core:0009_platform_display_pairing lets a pairing request
  name no module. It relaxes module_id and permission_id and adds a
  both-or-neither check. It is additive and destroys nothing.
- POST /api/v1/device-pairing/requests accepts {} for a platform
  display. Approval accepts an optional moduleId, so the administrator
  can choose an installed display module and the device gets that
  module's declared permission. A module display's own request can't be
  redirected.
- GET /api/v1/device-pairing/self lets a paired device describe itself:
  its name and the module displays it may show. It renews the device's
  cookie.
- GET /api/v1/devices/setup is replaced by
  GET /api/v1/devices/display-modules: the modules a display can be set
  to show.
- Settings -> Displays always offers the /display/setup address, Copy
  setup link and Add display. Add display has an optional "Show on this
  screen" choice, and each paired display says what it shows.
- /display/<module-id> is unchanged, so released Signage 0.1.5 works as
  before.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/api/tests/lifecycle.test.ts

@@ -24,8 +24,16 @@ vi.mock("../src/dashboard-host-assets.js", async (importOriginal) => {
   );
   return { ...actual, loadDashboardHostAssets: loadDashboardHostAssetsMock };
 });
+// Every startup also reads the built display host, because every installation serves the platform's
+// `/display/setup` page (ADR 0065), so this loader answers a small consistent snapshot too.
+const defaultDisplayHostAssets = vi.hoisted(() => ({ factory: undefined as unknown }));
 vi.mock("../src/display-host-assets.js", async (importOriginal) => {
   const actual = await importOriginal<typeof import("../src/display-host-assets.js")>();
+  defaultDisplayHostAssets.factory = () =>
+    actual.createDisplayHostAssets("<!doctype html>", "export {};\n", "export {};\n");
+  loadDisplayHostAssetsMock.mockImplementation(async () =>
+    (defaultDisplayHostAssets.factory as () => unknown)(),
+  );
   return { ...actual, loadDisplayHostAssets: loadDisplayHostAssetsMock };
 });
 // Wraps the real `createApiApp` in a spy rather than replacing it, so every existing test still
@@ -1096,6 +1104,9 @@ describe("Ekklesia API module runtime startup and shutdown", () => {
     drizzleAdapterMock.mockClear();
     serveMock.mockReset();
     loadDisplayHostAssetsMock.mockReset();
+    loadDisplayHostAssetsMock.mockImplementation(async () =>
+      (defaultDisplayHostAssets.factory as () => unknown)(),
+    );
     vi.mocked(createApiApp).mockClear();
   });
 
@@ -1159,7 +1170,7 @@ describe("Ekklesia API module runtime startup and shutdown", () => {
     expect(serveMock).not.toHaveBeenCalled();
   });
 
-  it("does not read display-host assets when the eligible set declares no display", async () => {
+  it("reads display-host assets even when no module declares a display, for /display/setup (ADR 0065)", async () => {
     const modulesDirectory = await createTemporaryModulesDirectory();
     const recorder = createEventRecorder();
     await createWorkingFixtureModule(modulesDirectory, "calendar", recorder);
@@ -1168,7 +1179,8 @@ describe("Ekklesia API module runtime startup and shutdown", () => {
 
     const running = await startApi(validConfig(), { modulesDirectoryOverride: modulesDirectory });
 
-    expect(loadDisplayHostAssetsMock).not.toHaveBeenCalled();
+    // A screen can be set up on any installation, whatever is installed.
+    expect(loadDisplayHostAssetsMock).toHaveBeenCalledTimes(1);
     await running.shutdown();
   });