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]>

scripts/lib/deploy-smoke-client.mjs

@@ -115,6 +115,30 @@ async function edgeChecks() {
     );
   }
 
+  // ADR 0065: a new screen can start pairing at the platform's own setup page whatever is
+  // installed — in the same-origin smoke, with no module at all — and asks to be paired with no
+  // module, as a platform display.
+  const setupPage = await fetch(`${apiOrigin}/display/setup`);
+  const setupHtml = await setupPage.text();
+  check(
+    setupPage.status === 200 &&
+      setupPage.headers.get("cache-control") === "no-store" &&
+      setupHtml.includes('id="ekklesia-display"'),
+    "GET /display/setup through the proxy is the platform display setup page",
+  );
+  const platformPairing = await fetch(`${apiOrigin}/api/v1/device-pairing/requests`, {
+    body: "{}",
+    headers: { "content-type": "application/json", origin: apiOrigin },
+    method: "POST",
+  });
+  const platformPairingBody = await platformPairing.json().catch(() => ({}));
+  check(
+    platformPairing.status === 201 &&
+      /^[0-9]{6}$/u.test(String(platformPairingBody.code)) &&
+      /HttpOnly/iu.test(platformPairing.headers.get("set-cookie") ?? ""),
+    "a screen at /display/setup can ask to be paired as a platform display, with no module",
+  );
+
   const script = await fetch(`${dashboardOrigin}/assets/ekklesia-dashboard/app.js`);
   await script.arrayBuffer();
   check(script.status === 200, "GET /assets/ekklesia-dashboard/app.js is 200");