Explain display setup in Settings, stop iOS form zoom, lock the page behind the drawer

A second real-iPhone review of the Stage 1 Dashboard found three
defects. This fixes them, and ADR 0065 records the decisions.

- Settings -> Displays now sets up a screen in one place. A "Set up a
  new screen" panel shows the platform display page to open on the
  screen, a Copy link button, and Add display directly beneath it; the
  step-by-step version is folded into a <details>. The addresses come
  from a new GET /api/v1/devices/setup, which requires
  core.devices.manage and lists each running display module's
  /display/<module-id> page. Nothing names Signage. With no display
  module installed, the panel says so and offers no Add display.
- iOS Safari zoomed into the pairing field because the shared
  .ek-control rendered at 14px. On phones and touch screens it now
  renders at max(1rem, 16px). The viewport is untouched, so zoom stays
  available, and a test guards that. The shared focus trap now returns
  focus with preventScroll, so closing a dialog no longer moves the page
  under the phone header.
- While the phone drawer is open, the page behind it no longer scrolls.
  The root's overflow is hidden, a non-passive touchmove listener
  cancels drags outside the drawer's list and overscroll past its ends,
  and root overscroll is turned off. The list itself still scrolls.
  Closing restores the exact scroll position unless another page opened.

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

surfaces/shell/tests/viewport.test.ts

@@ -0,0 +1,35 @@
+import { readFile } from "node:fs/promises";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+import { describe, expect, it } from "vitest";
+
+/**
+ * Zoom stays available to everyone who needs it (ADR 0065). iOS Safari's zoom into small form
+ * fields is fixed by the fields' own font size, never by locking the viewport.
+ */
+const packageDirectory = path.dirname(path.dirname(fileURLToPath(import.meta.url)));
+
+async function viewport(page: string): Promise<string> {
+  const html = await readFile(path.join(packageDirectory, page), "utf8");
+  const tag = /<meta\s+content="([^"]*)"\s+name="viewport"\s*\/?>/u.exec(html);
+  if (!tag?.[1]) {
+    throw new Error(`${page} has no viewport tag`);
+  }
+  return tag[1];
+}
+
+describe("the shell's pages never disable zoom", () => {
+  for (const page of ["index.html", "display.html"]) {
+    it(`${page} allows pinch and accessibility zoom`, async () => {
+      const content = (await viewport(page)).replace(/\s+/gu, "");
+      expect(content).toContain("width=device-width");
+      expect(content).not.toMatch(/user-scalable=(no|0)/iu);
+      expect(content).not.toMatch(/maximum-scale/iu);
+      expect(content).not.toMatch(/minimum-scale/iu);
+    });
+  }
+
+  it("lets the Dashboard lay itself out around a notch", async () => {
+    expect(await viewport("index.html")).toContain("viewport-fit=cover");
+  });
+});