Add Docker/Compose setup and fix subpath routing for /toroid deployment

- Add Dockerfile, .dockerignore, and docker-compose.yml to containerize the app
- Add toroid.service systemd unit (uses docker compose)
- Mount presets/ as a bind volume for persistence outside the container
- Fix all fetch() calls in templates to use relative paths (no leading /)
  so they resolve correctly when served under /toroid/ via nginx proxy

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

Dockerfile

@@ -0,0 +1,12 @@
+FROM python:3.12-slim
+
+WORKDIR /app
+
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY . .
+
+EXPOSE 5010
+
+CMD ["python", "app.py"]