feat: implement automated Docker deployment and update README

- Replaced manual rsync/npm_deploy workflow with multi-stage Docker builds.
- Added Dockerfile and .dockerignore for staging and production environments.
- Added 'deploy:staging' and 'deploy:prod' scripts to package.json.
- Updated README.md with new deployment instructions.

Dockerfile

@@ -0,0 +1,46 @@
+# Stage 1: Build the application
+# Using node:21-alpine for a lightweight, secure build environment.
+FROM node:21-alpine AS builder
+WORKDIR /app
+
+# Install dependencies first for better Docker layer caching.
+# This step only reruns if package.json or package-lock.json changes.
+COPY package*.json ./
+RUN npm install
+
+# Copy the rest of the source code.
+COPY . .
+
+# Build Argument to determine build environment (staging, prod, or production).
+# Defaults to "staging".
+ARG BUILD_MODE=staging
+ENV NODE_ENV=production
+
+# Perform the build based on the BUILD_MODE argument.
+# This runs the existing scripts in package.json, which already
+# handle copying the correct .env file to .env.production for Vite.
+RUN if [ "$BUILD_MODE" = "prod" ] || [ "$BUILD_MODE" = "production" ]; then \
+        npm run build:prod; \
+    else \
+        npm run build:staging; \
+    fi
+
+# Stage 2: Final runtime image
+FROM node:21-alpine AS deploy-node
+WORKDIR /app
+
+# Copy only the built files and necessary scripts from the builder stage.
+COPY --from=builder /app/build .
+COPY --from=builder /app/package.json .
+
+# Install only production dependencies for a smaller, cleaner image.
+RUN npm install --omit=dev
+
+# Copy the resulting .env.production file to .env.
+# adapter-node reads from .env at runtime for non-PUBLIC_ variables.
+COPY --from=builder /app/.env.production .env
+
+# SvelteKit (via adapter-node) defaults to port 3000.
+EXPOSE 3000
+
+CMD ["node", "index.js"]