feat(client): generic shared-wallet shim surface (docs/storeRegistry/isolation/accounts)

Port the shared-wallet shim mechanics from the Festipod app into the
generic @ng-eventually/client library — zero app-specific knowledge, the
consumer injects the domain (entity->scope mapping, connections, storage).

New namespaces exposed from src/index.ts:
- docs      docCreate/sparqlUpdate/sparqlQuery via the REAL injected `ng`
            (getConfig().ng), never the public makeNg proxy — the JS-over-
            iframe double proxy breaks doc_create postMessage marshaling
            (DataCloneError). Validated hard constraint.
- storeRegistry  generic (account,scope)->NURI resolver, createEntityDoc/
            listEntityDocs + per-scope index, sharedWalletShim in the
            private_store, cache. Consumer wiring injected via
            configureStoreRegistry({ getSession, normalizeUser }).
- isolation  pure applyIsolation (public=all / protected=owner+connections
            / private=owner); accessors + connection graph injected.
- accounts  AccountStore (localStorage-backed faux login, storage injected)
            + normalizeUsername. React wrapper intentionally NOT ported.

polyfill.ts gains configureStoreRegistry/getStoreRegistryDeps + resetConfig.
36/36 bun test, tsc --noEmit rc=0.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/client/src/index.ts

@@ -15,6 +15,13 @@ export * from "./types";
 export { useShape } from "./use-shape";
 export { init, initNg } from "./lifecycle";
 export * as inbox from "./inbox";
+export * as docs from "./docs";
+export * as storeRegistry from "./store-registry";
+export type { AccountRecord, RegistrySession } from "./store-registry";
+export * as isolation from "./isolation";
+export type { Connections, IsolationAccessors } from "./isolation";
+export * as accounts from "./accounts";
+export type { AccountStorage } from "./accounts";
 
 // SDK type re-exports — so the app imports these from @ng-eventually/client too,
 // not from @ng-org. `export type` is ERASED at build, so this adds NO runtime