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/api-http.integration.ts

@@ -1,5 +1,5 @@
 import { randomBytes } from "node:crypto";
-import { mkdir, mkdtemp, rm, writeFile } from "node:fs/promises";
+import { mkdir, mkdtemp, readFile, rm, writeFile } from "node:fs/promises";
 import { request as httpRequest } from "node:http";
 import net from "node:net";
 import { tmpdir } from "node:os";
@@ -26,8 +26,13 @@ import {
 import { Client, type QueryResultRow } from "pg";
 import { afterAll, describe, expect, it, vi } from "vitest";
 import type { ClientAddressConfigInput } from "../src/client-address.js";
+import { dashboardHostAssetUrls } from "@ekklesia/shell/dashboard-assets";
 import { createApiRuntimeConfig } from "../src/config.js";
 import { createApiDatabase } from "../src/database.js";
+import {
+  DASHBOARD_HOST_PAGE_PATH,
+  DASHBOARD_HOST_SCRIPT_PATH,
+} from "../src/dashboard-host-routes.js";
 import {
   HEALTH_LIVE_PATH,
   HEALTH_READY_PATH,
@@ -2983,6 +2988,48 @@ describe.sequential("live API — published module UI artifact", () => {
   });
 });
 
+describe.sequential("live API — the built Dashboard on the API's own origin", () => {
+  it("serves the built shell's exact index.html at / and its exact script, and nothing beside them", async () => {
+    const database = await createDisposableDatabase("dashboard_host");
+    await applyCoreMigrations(database.url);
+    const running = await startMigratedApi(database.url);
+    try {
+      const origin = apiOrigin(running);
+      const builtHtml = await readFile(new URL(dashboardHostAssetUrls.html), "utf8");
+      const builtScript = await readFile(new URL(dashboardHostAssetUrls.script), "utf8");
+
+      const page = await fetch(`${origin}${DASHBOARD_HOST_PAGE_PATH}`);
+      const html = await page.text();
+      expect(page.status).toBe(200);
+      expect(page.headers.get("content-type")).toBe("text/html; charset=utf-8");
+      expect(page.headers.get("cache-control")).toBe("no-cache");
+      expect(page.headers.get("x-frame-options")).toBe("DENY");
+      expect(page.headers.get("content-security-policy")).toBe("frame-ancestors 'none'");
+      expect(page.headers.get("referrer-policy")).toBe("no-referrer");
+      expect(html).toBe(builtHtml);
+      expect(html).toContain('id="ekklesia-host"');
+      expect(html).toContain(`<script src="${DASHBOARD_HOST_SCRIPT_PATH}" type="module"></script>`);
+
+      const revalidated = await fetch(`${origin}${DASHBOARD_HOST_PAGE_PATH}`, {
+        headers: { "if-none-match": page.headers.get("etag") ?? "" },
+      });
+      expect(revalidated.status).toBe(304);
+
+      const script = await fetch(`${origin}${DASHBOARD_HOST_SCRIPT_PATH}`);
+      expect(script.status).toBe(200);
+      expect(script.headers.get("content-type")).toBe("text/javascript; charset=utf-8");
+      expect(await script.text()).toBe(builtScript);
+
+      // The source map sits beside the script on disk and is never published.
+      const sourceMap = await fetch(`${origin}${DASHBOARD_HOST_SCRIPT_PATH}.map`);
+      expect(sourceMap.status).toBe(404);
+      expect(await sourceMap.json()).toEqual({ code: "NOT_FOUND" });
+    } finally {
+      await running.shutdown();
+    }
+  });
+});
+
 describe.sequential("live API — health", () => {
   it("answers liveness and readiness with 200 against a migrated disposable PostgreSQL", async () => {
     const database = await createDisposableDatabase("health");