feat(tests): add unit and integration test suite (node:test)

Adds 215 tests across three tiers using node:test + node:assert/strict
(no new test framework dependencies):

- test/tools/ — middleware and utility tests (token, hash, authenticate,
  jsonBody, convertError, validators)
- test/shared/ — DbInterface/BackendDbInterface contract suites reusable
  across backends (users, abodes, residents, apikeys, sessions, auth)
- test/backends/sqlite/ — SQLite-private tests (sql builder, WrappedDb,
  migrator) + shared suites via SqliteInterface
- test/backends/api/ — ApiInterface unit tests + shared suites via a
  live Koa server backed by SQLite

Also fixes four bugs uncovered by the tests:
- ApiInterface: path params leaked into query string (slice(1) fix)
- ApiInterface: calling res.json() on 204 No Content responses
- SqliteInterface.updateResident: missing comma in SET clause
- WrappedBetterSqlite3Db: readonly:undefined rejected by better-sqlite3

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/backends/api/index.test.ts

@@ -0,0 +1,39 @@
+import { createTestDb } from "../../helpers/sqlite.js";
+import { createTestServer } from "../../helpers/koa.js";
+import { ApiInterface } from "../../../src/db/api/ApiInterface.js";
+import { hashPassword } from "../../../src/util/hash.js";
+import { runUserTests } from "../../shared/users.js";
+import { runAbodeTests } from "../../shared/abodes.js";
+import { runResidentTests } from "../../shared/residents.js";
+import { runApikeyTests } from "../../shared/apikeys.js";
+
+const AUTH_EMAIL = "api-auth@test.example";
+const AUTH_PASSWORD = "api-auth-password";
+
+async function getApiDb() {
+  const { db: sqliteDb, close: closeSqlite } = await createTestDb();
+  const pw = await hashPassword(AUTH_PASSWORD);
+  await sqliteDb.createUser({
+    email: AUTH_EMAIL,
+    name: "API Auth User",
+    password: pw,
+    flags: {},
+  });
+  const server = await createTestServer(sqliteDb);
+  const authHeader = "Basic " + btoa(`${AUTH_EMAIL}:${AUTH_PASSWORD}`);
+  const api = new ApiInterface(server.url, {
+    headers: { Authorization: authHeader },
+  });
+  return {
+    db: api,
+    close: async () => {
+      await server.close();
+      closeSqlite();
+    },
+  };
+}
+
+runUserTests("api", getApiDb);
+runAbodeTests("api", getApiDb);
+runResidentTests("api", getApiDb);
+runApikeyTests("api", getApiDb);