feat: mount discovered module UI in a minimal Ekklesia browser host

Phase 6C pass 2. Every link in the module UI chain existed except the one
that closes it: a module could be authored, built, validated, published at a
browser URL, and loaded by a generic loader — and nothing in Ekklesia did any
of it. There was no browser application at all.

Two pieces were missing. A browser could not discover what to mount, and it
must not work that out for itself.

GET /api/v1/module-ui is the inventory: per publishable module, its id and
version, the server-produced artifact URL, the server-produced root of the
module's own API, and the subset of that module's declared permissions the
caller holds. Five fields, each because building a ModuleUiHostContext needs
it — no filesystem paths, and no name/icon/folder/order, because navigation
metadata is a design that does not exist yet. Its module set is the ADR 0025
publication registry rather than a rescan, so the inventory and the artifact
route cannot disagree. It requires a new Core permission, core.modules.ui.read
(baseline authenticated), because it is precisely the enumeration the anonymous
artifact route deliberately withholds.

Both URLs are server-produced. moduleUiArtifactUrl already existed;
moduleApiBaseUrl is now exported and moduleRoutePath builds on it, so each URL
shape has exactly one author. Without it the shell would hardcode
/api/v1/modules/<id> — the prefix ADR 0022 forbids a module UI from spelling,
reappearing in the host instead.

surfaces/shell (@ekklesia/shell) is the repository's first surface: a small
React application built to static files by its own esbuild script. It resolves
the principal, fetches the inventory, builds the host context entirely from
server-derived data, and hands the artifact URL to @ekklesia/module-ui-host.
One frame per selection — keyed by module identity — defeats the stale-load
race; the host owns the container, the loading state, and every failure, so a
broken module costs its own panel rather than the shell.

The shell statically imports no module, and both levels are checked: no source
import may name a module, and the emitted bundle must contain exactly one
dynamic import (the loader's) with no module id, no /api/v1/modules, no eval,
and no blob URL. Permission hints come from Core's own evaluator and stay
presentation-only — the end-to-end test has a UI holding no grant call its API
anyway and still receive 403.

Surfaces may now depend only on browser-safe shared roles; @ekklesia/contracts
is deliberately excluded, since its barrel pulls Drizzle's types and Node's
globals into the browser — the hole ADR 0024 closed one layer down.

Not the Dashboard: no navigation, grouping, icons, ordering, design system, or
routing. The selector is a list of module ids.

Co-Authored-By: Claude Opus 5 <[email protected]>

surfaces/shell/src/browser/main.tsx

@@ -0,0 +1,31 @@
+import { createRoot } from "react-dom/client";
+import type { EkklesiaHostConfig } from "../host-protocol.js";
+import { HostApp } from "./HostApp.js";
+
+/**
+ * Replaced at build time by `scripts/build-browser.mjs` with a JSON string literal: the API origin
+ * when `EKKLESIA_API_BASE_URL` was set for the build, and `""` otherwise. Declared rather than read
+ * from `process.env`, because a browser has no `process` and the substitution must be visible here
+ * instead of hidden in bundler configuration.
+ */
+declare const __EKKLESIA_API_BASE_URL__: string;
+
+/**
+ * The one place the shell touches a browser global.
+ *
+ * An empty build-time value means the API is served from the same origin as this page, which is the
+ * expected production shape; a non-empty one is the split-origin development shape the platform's
+ * trusted-origin configuration already supports (`EKKLESIA_IDENTITY_TRUSTED_ORIGINS` must list this
+ * page's origin for the session cookie to travel). Everything downstream receives the resolved
+ * origin as a plain argument, so no other file in this package reads `window`.
+ */
+const config: EkklesiaHostConfig = {
+  apiBaseUrl: __EKKLESIA_API_BASE_URL__ || window.location.origin,
+};
+
+const container = document.getElementById("ekklesia-host");
+if (!container) {
+  throw new Error("The Ekklesia shell requires a #ekklesia-host element.");
+}
+
+createRoot(container).render(<HostApp config={config} />);