Add Dockerfile for containerized build and update package.json with start script for development server

Dockerfile

@@ -0,0 +1,16 @@
+FROM node:22-alpine AS builder
+
+WORKDIR /pomoday
+
+COPY package.json .
+
+RUN npm install --global corepack@latest
+RUN corepack enable pnpm
+
+RUN pnpm install
+
+COPY . .
+
+RUN pnpm run build
+
+CMD pnpm run start