chore: migrate deployment to Dockerfile

Replace nixpacks.toml with a multi-stage Dockerfile (node:22-alpine builder + nginx:alpine runner) for faster Coolify deployments.

Dockerfile

@@ -0,0 +1,18 @@
+FROM node:22-alpine AS builder
+
+WORKDIR /app
+
+RUN corepack enable && corepack prepare pnpm@latest --activate
+
+COPY package.json pnpm-lock.yaml ./
+RUN pnpm install --frozen-lockfile
+
+COPY . .
+RUN pnpm run build
+
+FROM nginx:alpine
+
+COPY --from=builder /app/dist /usr/share/nginx/html
+
+EXPOSE 80
+CMD ["nginx", "-g", "daemon off;"]