fix(tests): address review gaps in test suite

- Add tsconfig.test.json + typecheck:test script so test/ is type-checked;
  fixes real type errors it surfaced (hashedPw typing, PartialUser|ClientUser
  narrowing for .email).
- Add HTTP-level auth-http.test.ts for the api backend covering
  login/session-cookie/logout/clear-sessions/bearer-apikey flows, since
  ApiInterface doesn't implement the session/login methods needed to run the
  shared session/auth suites directly.
- Make the readonly-db test in shared/users.ts actually construct a readonly
  db instance (previously a no-op that never ran) via a new getReadonlyDb
  parameter, wired up for both sqlite and api backends.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

test/helpers/sqlite.ts

@@ -16,3 +16,9 @@ export async function createTestDb(): Promise<TestDb> {
   const db = new SqliteInterface(wrapped);
   return { db, wrapped, close: () => wrapped.destroy() };
 }
+
+export async function createReadonlyTestDb(): Promise<TestDb> {
+  const wrapped = getWrappedDb("node", ":memory:", { readonly: true });
+  const db = new SqliteInterface(wrapped);
+  return { db, wrapped, close: () => wrapped.destroy() };
+}