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/test/accounts.test.ts

@@ -0,0 +1,84 @@
+import { test, expect } from "bun:test";
+import {
+  AccountStore,
+  browserAccountStore,
+  normalizeUsername,
+  ACCOUNT_STORAGE_KEY,
+  type AccountStorage,
+} from "../src/accounts";
+
+// In-memory fake of the Storage subset — keeps this framework/DOM-agnostic.
+function fakeStorage(): AccountStorage & { map: Map<string, string> } {
+  const map = new Map<string, string>();
+  return {
+    map,
+    getItem: (k) => (map.has(k) ? (map.get(k) as string) : null),
+    setItem: (k, v) => void map.set(k, v),
+    removeItem: (k) => void map.delete(k),
+  };
+}
+
+test("normalizeUsername: strips leading @, trims, lowercases", () => {
+  expect(normalizeUsername("marie")).toBe("marie");
+  expect(normalizeUsername("@Marie")).toBe("marie");
+  expect(normalizeUsername("  @@MARIE  ")).toBe("marie");
+  expect(normalizeUsername(null)).toBe("");
+  expect(normalizeUsername(undefined)).toBe("");
+});
+
+test("AccountStore: login persists a trimmed username, get reads it back", () => {
+  const s = fakeStorage();
+  const store = new AccountStore(s);
+  expect(store.get()).toBeNull();
+
+  expect(store.login("  Marie ")).toBe("Marie"); // trimmed, NOT normalized (display form)
+  expect(store.get()).toBe("Marie");
+  expect(s.map.get(ACCOUNT_STORAGE_KEY)).toBe("Marie");
+});
+
+test("AccountStore: blank login is ignored, keeps the previous value", () => {
+  const store = new AccountStore(fakeStorage());
+  store.login("bob");
+  expect(store.login("   ")).toBe("bob");
+  expect(store.get()).toBe("bob");
+});
+
+test("AccountStore: logout clears the username (no throw)", () => {
+  const store = new AccountStore(fakeStorage());
+  store.login("bob");
+  store.logout();
+  expect(store.get()).toBeNull();
+});
+
+test("AccountStore: null storage degrades to non-persisting (SSR-safe)", () => {
+  const store = new AccountStore(null);
+  expect(store.get()).toBeNull();
+  expect(store.login("bob")).toBe("bob"); // returns the value, just doesn't persist
+  expect(store.get()).toBeNull();
+  store.logout(); // no throw
+});
+
+test("AccountStore: swallows storage errors on read and write", () => {
+  const throwing: AccountStorage = {
+    getItem: () => {
+      throw new Error("boom");
+    },
+    setItem: () => {
+      throw new Error("boom");
+    },
+    removeItem: () => {
+      throw new Error("boom");
+    },
+  };
+  const store = new AccountStore(throwing);
+  expect(store.get()).toBeNull(); // read error swallowed → null
+  expect(() => store.login("bob")).not.toThrow();
+  expect(() => store.logout()).not.toThrow();
+});
+
+test("browserAccountStore returns a working store (uses global localStorage if present)", () => {
+  const store = browserAccountStore("ng-eventually.test.account");
+  expect(store).toBeInstanceOf(AccountStore);
+  // Behaves regardless of environment: login returns the value.
+  expect(store.login("zoe")).toBe("zoe");
+});