refactor(docker): rework docker

- Move Docker files to own directory (tidier since I added several more files)
- Optimise images and reduce size
  - Uses multi-stage builds
  - Optimises layer efficiency
  - Uses NGINX as base for frontend
- Sets default env vars
- Uses tini for proper signal handling

frontend/Dockerfile

@@ -1,16 +0,0 @@
-FROM node:lts-alpine
-
-WORKDIR /app
-
-COPY package*.json ./
-
-RUN npm install
-
-COPY . .
-
-RUN npm run build
-RUN npm install --only=production
-
-EXPOSE 3000
-
-CMD ["node", "server.js"]