feat(api): serve the built Dashboard from the API origin

Serve surfaces/shell's built Dashboard from apps/api on the same origin
as /api (ADR 0044), exactly as the display host is served: a closed set
of files read once at startup, never a static directory, never a path
built from request input.

- The shell exports @ekklesia/shell/dashboard-assets (the exact built
  index.html and script URLs), emits the script at
  assets/ekklesia-dashboard/app.js, and index.html names that absolute
  path so dev and production serve the same URLs.
- GET / and GET /assets/ekklesia-dashboard/app.js answer from a frozen
  snapshot: no-cache with a strong ETag and 304 on match. Source maps
  are never served; every other path is the ordinary sanitized 404.
- The page sets nosniff, X-Frame-Options: DENY, Content-Security-Policy:
  frame-ancestors 'none' (that directive only), and Referrer-Policy:
  no-referrer, on 200 and 304 alike.
- A missing or empty shell build fails startup with a fixed
  DashboardHostAssetError before any module code is imported.
- The If-None-Match comparison moves to conditional-request.ts, shared
  with the display host routes.
- The emailed-link token stripping moves from browser/main.tsx into
  consumeAuthLanding (location and history injected) so it is tested;
  behavior is unchanged.

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

apps/api/tests/lifecycle.test.ts

@@ -9,11 +9,21 @@ const drizzleAdapterMock = vi.hoisted(() => vi.fn());
 const serveMock = vi.hoisted(() => vi.fn());
 const processOnSpy = vi.hoisted(() => vi.fn());
 const loadDisplayHostAssetsMock = vi.hoisted(() => vi.fn());
+const loadDashboardHostAssetsMock = vi.hoisted(() => vi.fn());
 
 vi.mock("pg", () => ({ Pool: poolConstructor }));
 vi.mock("better-auth", () => ({ betterAuth: betterAuthMock }));
 vi.mock("better-auth/adapters/drizzle", () => ({ drizzleAdapter: drizzleAdapterMock }));
 vi.mock("@hono/node-server", () => ({ serve: serveMock }));
+// Every startup reads the built Dashboard (ADR 0044), and this file never depends on a built shell,
+// so the loader answers a small consistent snapshot unless a test makes it fail.
+vi.mock("../src/dashboard-host-assets.js", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("../src/dashboard-host-assets.js")>();
+  loadDashboardHostAssetsMock.mockImplementation(async () =>
+    actual.createDashboardHostAssets("<!doctype html>", "export {};\n"),
+  );
+  return { ...actual, loadDashboardHostAssets: loadDashboardHostAssetsMock };
+});
 vi.mock("../src/display-host-assets.js", async (importOriginal) => {
   const actual = await importOriginal<typeof import("../src/display-host-assets.js")>();
   return { ...actual, loadDisplayHostAssets: loadDisplayHostAssetsMock };
@@ -35,6 +45,7 @@ import {
 import { PermissionRegistryError } from "@ekklesia/core/authorization";
 import { createApiApp } from "../src/app.js";
 import { createApiRuntimeConfig } from "../src/config.js";
+import { DashboardHostAssetError } from "../src/dashboard-host-assets.js";
 import { DisplayHostAssetError } from "../src/display-host-assets.js";
 import {
   HEALTH_LIVE_PATH,
@@ -1057,6 +1068,30 @@ describe("Ekklesia API module runtime startup and shutdown", () => {
     expect(serveMock).not.toHaveBeenCalled();
   });
 
+  it("fails on missing Dashboard assets before importing module code and still closes startup resources", async () => {
+    const modulesDirectory = await createTemporaryModulesDirectory();
+    const recorder = createEventRecorder();
+    await createWorkingFixtureModule(modulesDirectory, "calendar", recorder);
+    const { poolEnd } = mockPoolAndAuth();
+    loadDashboardHostAssetsMock.mockRejectedValueOnce(new DashboardHostAssetError());
+
+    const failure = await startApi(validConfig(), {
+      modulesDirectoryOverride: modulesDirectory,
+    }).catch((error: unknown) => error);
+
+    expect(failure).toMatchObject({
+      code: "DASHBOARD_HOST_ASSET_UNAVAILABLE",
+      message: "The Dashboard host browser assets are unavailable.",
+      name: "DashboardHostAssetError",
+    });
+    expect((failure as Error).stack).toBe(
+      "DashboardHostAssetError: The Dashboard host browser assets are unavailable.",
+    );
+    expect(recorder.events).toEqual([]);
+    expect(poolEnd).toHaveBeenCalledTimes(1);
+    expect(serveMock).not.toHaveBeenCalled();
+  });
+
   it("does not read display-host assets when the eligible set declares no display", async () => {
     const modulesDirectory = await createTemporaryModulesDirectory();
     const recorder = createEventRecorder();