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>

docker-compose.yml

@@ -0,0 +1,8 @@
+services:
+  toroid:
+    build: .
+    ports:
+      - "5010:5010"
+    volumes:
+      - ./presets:/app/presets
+    restart: unless-stopped