test(integration): dockerized webmail⇆Stalwart Playwright sync suite

Add an end-to-end integration harness that runs the webmail against a real
Stalwart mail server in Docker and drives it with Playwright, focused on the
mail/folder synchronisation behaviour (unread/total counters, folder-list
sync, account-scoped Unified Mailbox) that the unified-mailbox work touches.

- integration/ stack: Stalwart (declarative bootstrap: alice/bob/carol,
  submission + IMAP listeners, permissive CORS) + webmail (dev mode, so the
  browser's plaintext cross-origin JMAP calls aren't blocked by the prod CSP).
- Helpers: dependency-free SMTP submit client, JMAP client for seeding /
  inspecting server state, and page helpers (login, add/switch account,
  locale-independent folder-counter reads).
- Specs: login, single-account sync (receive/read/move/delete/folder-create/
  burst) and multi-account (per-account isolation + cross-account Unified
  Inbox aggregation + background-account delivery). 12 tests, all green.
- Add focused data-testid hooks to the mail UI (folder rows + counters, email
  list items, account switcher, composer) for stable selectors.
- Exclude examples/ and integration/ from tsconfig/eslint/.dockerignore.

integration/tests/helpers/config.ts

@@ -0,0 +1,45 @@
+/**
+ * Shared configuration for the integration tests. Values mirror the Stalwart
+ * bootstrap (integration/stalwart/*) and the docker-compose port mappings.
+ * Everything is overridable via env so the suite can run against a differently
+ * mapped stack (e.g. remote CI) without code changes.
+ */
+
+export const DOMAIN = process.env.IT_DOMAIN ?? 'example.org';
+
+/** Shared password for every test mailbox (TEST_ACCOUNT_PASSWORD in .env). */
+export const ACCOUNT_PASSWORD = process.env.IT_ACCOUNT_PASSWORD ?? 'test-pass-123';
+
+/** Webmail app origin (containerised, published on the host). */
+export const WEBMAIL_URL = process.env.IT_WEBMAIL_URL ?? 'http://localhost:3000';
+
+/** Stalwart JMAP + admin base URL (host-published). */
+export const JMAP_URL = process.env.IT_JMAP_URL ?? 'http://localhost:8025';
+
+/** Stalwart SMTP submission listener (host-published, maps to container 587). */
+export const SMTP_HOST = process.env.IT_SMTP_HOST ?? 'localhost';
+export const SMTP_PORT = Number(process.env.IT_SMTP_PORT ?? 1025);
+
+/** Recovery admin — `user:password`, used for stalwart-cli style admin JMAP. */
+export const ADMIN_CREDENTIALS = process.env.IT_ADMIN ?? 'admin:bootstrap-secret';
+
+export interface TestAccount {
+  /** Local part, e.g. "alice". */
+  user: string;
+  /** Full address, e.g. "alice@example.org". */
+  email: string;
+  password: string;
+}
+
+function acct(user: string): TestAccount {
+  return { user, email: `${user}@${DOMAIN}`, password: ACCOUNT_PASSWORD };
+}
+
+/** The mailboxes provisioned by the Stalwart bootstrap plan. */
+export const ACCOUNTS = {
+  alice: acct('alice'),
+  bob: acct('bob'),
+  carol: acct('carol'),
+} as const;
+
+export type AccountKey = keyof typeof ACCOUNTS;