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/src/app.ts

@@ -27,6 +27,8 @@ import type { Context, MiddlewareHandler } from "hono";
 import { Hono } from "hono";
 import { cors } from "hono/cors";
 import { AUTH_REQUEST_MAX_BODY_BYTES, platformBodyLimit } from "./body-limits.js";
+import type { DashboardHostAssets } from "./dashboard-host-assets.js";
+import { createDashboardHostRoutes } from "./dashboard-host-routes.js";
 import { createDashboardRoutes } from "./dashboard-routes.js";
 import { createDeviceRoutes } from "./device-routes.js";
 import type { DisplayHostAssets } from "./display-host-assets.js";
@@ -138,6 +140,13 @@ export interface CreateApiAppOptions {
    * presentation only — nothing reachable through this store influences discovery, dependency
    * ordering, module startup, or any authorization decision. */
   readonly dashboard: DashboardStore;
+  /**
+   * The built Dashboard's two files, read once by production startup (ADR 0044). Required rather
+   * than optional, unlike `displayHostAssets`: every installation has a Dashboard, and a missing
+   * shell build fails startup instead of leaving this origin answering `/` with a 404. See
+   * `./dashboard-host-routes.js`.
+   */
+  readonly dashboardHostAssets: DashboardHostAssets;
   /**
    * The readiness inputs behind the unauthenticated health routes (ADR 0044). Required rather than
    * defaulted, like every other dependency here: a composition that cannot reach a database says so
@@ -354,6 +363,11 @@ export function createApiApp(options: CreateApiAppOptions): Hono {
   // own entirely. See `./health-routes.js`.
   app.route("/", createHealthRoutes(options.health));
 
+  // The Dashboard page and its one script, at exact literal paths outside `/api/` (ADR 0044). They
+  // grant no authority and resolve no principal; the page asks `/api/v1/principal` itself. See
+  // `./dashboard-host-routes.js`.
+  app.route("/", createDashboardHostRoutes(options.dashboardHostAssets));
+
   app.route(
     "/",
     createGrantsRoutes({