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]>

scripts/check-boundaries.ts

@@ -235,6 +235,30 @@ function boundaryRule(from: Location, to: Location): string | undefined {
     if (to.layer === "surface" && from.owner !== to.owner) {
       return "surfaces-are-independent";
     }
+    // A surface is browser code, so the roles it may reach are the browser-safe ones plus dev-time
+    // tooling. `contracts` is deliberately absent even though it is a "public contract" package:
+    // its barrel pulls Drizzle's types, and with them Node's global declarations, into any program
+    // that imports it — measured in ADR 0024, which removed exactly that import from
+    // `@ekklesia/module-ui-sdk` to close the browser boundary. Allowing it here would reopen the
+    // same hole one layer up. `module-sdk` re-exports that barrel and is excluded for the same
+    // reason. A surface talks to the server over HTTP and validates what arrives; it does not share
+    // the server's type graph.
+    if (
+      to.layer === "shared" &&
+      ![
+        "api-client",
+        "auth-client",
+        "design-tokens",
+        "module-ui-host",
+        "module-ui-sdk",
+        "surface-sdk",
+        "testing",
+        "tooling",
+        "ui",
+      ].includes(to.role ?? "")
+    ) {
+      return "surfaces-use-public-contracts";
+    }
   }
 
   if (from.layer === "builder" && ["app", "core", "module", "surface"].includes(to.layer)) {