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

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

Dockerfile

@@ -0,0 +1,34 @@
+FROM python:3.11-slim
+
+RUN apt-get update -qq && \
+    apt-get install -y -q --no-install-recommends git && \
+    rm -rf /var/lib/apt/lists/*
+
+RUN pip install --no-cache-dir requests fastapi "uvicorn[standard]" pydantic
+
+ENV GIT_AUTHOR_NAME=outline-sync \
+    GIT_AUTHOR_EMAIL=sync@local \
+    GIT_COMMITTER_NAME=outline-sync \
+    GIT_COMMITTER_EMAIL=sync@local \
+    VAULT_DIR=/vault \
+    SETTINGS_PATH=/work/settings.json
+
+RUN git config --global user.email "sync@local" && \
+    git config --global user.name "outline-sync"
+
+WORKDIR /work
+
+COPY outline_sync.py webui.py settings.json ./
+
+# Initialise vault with both branches needed by outline_sync.py
+RUN git init /vault && \
+    git -C /vault checkout -b main && \
+    touch /vault/.gitkeep && \
+    git -C /vault add .gitkeep && \
+    git -C /vault commit -m "init: empty vault" && \
+    git -C /vault checkout -b outline && \
+    git -C /vault checkout main
+
+EXPOSE 8080
+
+CMD ["uvicorn", "webui:app", "--host", "0.0.0.0", "--port", "8080"]