feat: let one module contribute a browser renderer to another's capability

The platform has had a complete story for one module using another's
*backend* since ADR 0006 — capabilities, versioned ranges, provider
registration. It has had none at all for one module using another's *browser*
code, and every workaround is wrong in a way that matters: a consumer cannot
import a peer module, it cannot re-implement a renderer for a domain it does
not own, and a second `entrypoints` role would put the platform in charge of
deciding when a slot inside someone else's screen should be filled.

Add a generic browser contribution. `manifestVersion: 7` declares one:
namespaced id, its own version, a target capability, a compatible range, and
one artifact. That is the complete list, and the omissions are the decision —
no payload schema, slot, ordering, or rendering hint exists anywhere, so Core
cannot learn what a slide is because the declaration cannot express it.

Discovery resolves a contribution artifact through the *identical* loop every
other compiled entrypoint uses, inheriting the path, containment, symlink,
extension, and file-kind checks rather than getting a weaker copy of them. The
registry publishes one only when another eligible module provides the target
capability within the declared range; otherwise it is absent rather than
mounted and broken. `apps/api` serves it as a sibling of the artifact and
display routes, with the same policy: three lookup keys, one exact match, one
already-validated path, and one indistinguishable 404 for unknown, undeclared,
stale, and incompatible alike.

A consumer discovers through the host, never through a URL. Its descriptor
carries identity, version, and capability; the URL stays server-side and is
resolved exactly as `api.request("records")` is. A module can only ever see
contributions aimed at a capability it itself provides, and cannot name its
way to anything else — a mount for a withheld id fails without fetching.

The consumer owns the domain contract entirely. Input is opaque JSON, checked
structurally so a Date, a function, a cycle, or `undefined` fails at the
boundary rather than vanishing somewhere far from the mistake, and checked for
nothing else. A contributed renderer receives its own id and that input: no
API client, realtime, principal, configuration, database, storage, or
credential. Loading one grants its module nothing.

The contribution ABI is versioned separately from the module UI ABI, because
the two have different shapes and lifecycles and coupling them would force
every module to rebuild whenever either moved. It supports asynchronous
readiness, update-without-remount (a screen that remounted per tick would
restart animations and reload media), deterministic cleanup in a `finally`,
and sanitized failure that never carries the consumer's domain data. Each
renderer mounts in its own isolated root with its own stylesheet.

The template now declares a contribution, so `pnpm build` exercises the whole
authoring path, and the shell suite drives the full relationship — one module
discovering, mounting, updating, and unmounting another's React renderer with
neither importing the other.

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

docs/architecture/repository-boundaries.md

@@ -23,8 +23,8 @@ These rules map platform ownership to filesystem and package boundaries. The exe
   `@ekklesia/module-ui-sdk`. Since
   [ADR 0040](decisions/0040-module-stylesheets-and-artifact-isolation.md) it may also contain plain
   `.css`, but **only** inside a browser-artifact source root the canonical builder compiles
-  (`src/ui/`, `src/display/`); a stylesheet anywhere else in a module is a file no build reads and no
-  host loads. It still cannot contain `.jsx`, other stylesheet dialects, single-file components,
+  (`src/ui/`, `src/display/`, `src/contributions/`); a stylesheet anywhere else in a module is a file
+  no build reads and no host loads. It still cannot contain `.jsx`, other stylesheet dialects, single-file components,
   Astro/Marko/MDX/HTML views, or SVG presentation assets, and cannot depend on any other UI framework
   (including `react-router-dom`, `react-native`, and `@vitejs/plugin-react`) or on any shared role
   beyond the two approved design packages named below. A module needs no bundler plugin: `@ekklesia/module-ui-build` — a `tooling` package,
@@ -63,7 +63,19 @@ These rules map platform ownership to filesystem and package boundaries. The exe
   module code remains trusted, same-realm code. The browser mount ABI is versioned
   (`MODULE_UI_ABI_VERSION`) and a mismatched artifact fails closed rather than mounting under guessed
   semantics.
-- Manifest v6 permits independently optional primary (`entrypoints.ui`) and full-viewport display
+- A module may declare **browser contributions** (`manifest.contributions`, v7): compiled renderers
+  it offers to capabilities *other* modules provide
+  ([ADR 0041](decisions/0041-module-browser-contributions.md)). Core validates identity,
+  compatibility, and the artifact path through the identical resolution every other compiled
+  entrypoint uses, and knows nothing about what a contribution renders — there is no payload schema,
+  slot, ordering, or rendering hint anywhere in the platform. A contribution is published only when
+  another eligible module provides its target capability within the declared range; otherwise it is
+  absent rather than broken. A consuming module discovers contributions through
+  `ModuleUiHostContext.contributions` and mounts them by id; it never constructs a publication URL,
+  and it can only ever see contributions aimed at a capability it itself provides. A contributed
+  renderer receives its own id and the consumer's opaque JSON input, and no database, storage,
+  credential, session, or API client of its own.
+- Manifest v7 permits independently optional primary (`entrypoints.ui`) and full-viewport display
   (`entrypoints.display`) artifacts. Modules own both feature experiences; surfaces own their
   containers, routes, navigation/chrome, credentials, error states, and publication wiring. The
   fixed authoring sources are `src/ui/index.tsx` and `src/display/index.tsx`; both use the same