feat(backend): configure Dockerfile and express server to build and serve mobile app at /mobile on Cloud Run

backend/Dockerfile

@@ -5,12 +5,20 @@ RUN bun install
 COPY website/ .
 RUN bun run build
 
+FROM oven/bun:1.2.18 AS mobile-builder
+WORKDIR /mobile
+COPY mobile/package.json ./
+RUN bun install
+COPY mobile/ .
+RUN bun run build:web
+
 FROM oven/bun:1.2.18
 WORKDIR /app
 COPY backend/package.json backend/bun.lock backend/tsconfig.json ./
 RUN bun install --frozen-lockfile --production
 COPY backend/src ./src
 COPY --from=website-builder /website/dist ./public
+COPY --from=mobile-builder /mobile/dist ./public/mobile
 
 ENV NODE_ENV=production
 ENV PORT=8080