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/run-tests.sh

@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+# Run the Playwright integration suite.
+#
+# Playwright's browser download host is often unreachable (and some host OSes
+# aren't supported by the browser bundles), so the tests run inside the official
+# Playwright container, which ships the browsers. The container uses host
+# networking to reach the published stack ports (webmail :3000, Stalwart :8025).
+#
+# The docker stack itself is brought up here (on the host) and the in-container
+# run is told to skip its own docker management via IT_NO_DOCKER=1.
+#
+# Usage:
+#   integration/run-tests.sh                 # whole suite
+#   integration/run-tests.sh 01-login        # a single spec (grep on file name)
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+INTEGRATION_DIR="${REPO_ROOT}/integration"
+PW_IMAGE="mcr.microsoft.com/playwright:v1.59.1-noble"
+
+cd "${INTEGRATION_DIR}"
+[ -f .env ] || cp .env.example .env
+
+echo "== bringing up stack =="
+bash stalwart/prepare-stalwart-cli.sh
+docker compose --env-file .env up -d --build --wait --wait-timeout 300
+
+echo "== running Playwright in ${PW_IMAGE} =="
+FILTER="${1:-}"
+docker run --rm --network host \
+  --user "$(id -u):$(id -g)" \
+  -v "${REPO_ROOT}":/work -w /work \
+  -e IT_NO_DOCKER=1 \
+  -e HOME=/tmp \
+  "${PW_IMAGE}" \
+  npx playwright test -c playwright.integration.config.ts ${FILTER:+"$FILTER"}