Add sync engine, web UI, Docker setup, and tests

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

pytest.ini

@@ -0,0 +1,14 @@
+[pytest]
+asyncio_mode = auto
+testpaths = tests
+python_files = test_*.py
+python_classes = Test*
+python_functions = test_*
+
+markers =
+    integration: requires running infrastructure (WebDAV container, Outline API)
+    slow: longer-running tests
+
+filterwarnings =
+    ignore::DeprecationWarning:httpx
+    ignore::pytest.PytestUnraisableExceptionWarning