Add application, Dockerfile, CI workflow and documentation

- FastAPI-based Matrix chat export tool with E2E support
- Dockerfile with Python 3.12-slim base image
- Docker Compose with dedicated network configuration
- Gitea Actions workflow for automated image builds
- README with setup instructions and feature overview
- MIT license

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

Dockerfile

@@ -0,0 +1,18 @@
+FROM python:3.12-slim
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    libolm-dev gcc python3-dev \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY app/ ./app/
+
+RUN mkdir -p /app/exports /app/store
+
+EXPOSE 8080
+
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8080", "--log-level", "info"]