Fix Docker build: upgrade to node:22-alpine, install only server deps

The production stage was running npm ci --omit=dev against a macOS-
generated lockfile on linux/alpine, which caused exit code 1. Switch
to installing only the three packages the server actually needs
(express, cors, docx) so the lockfile is irrelevant in that stage.
Also upgrades to node:22-alpine (current LTS) to clear the Node 20
deprecation warning on GitHub Actions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -1,14 +1,13 @@
-FROM node:20-alpine AS build
+FROM node:22-alpine AS build
 WORKDIR /app
 COPY package*.json ./
 RUN npm ci
 COPY . .
 RUN npm run build
 
-FROM node:20-alpine
+FROM node:22-alpine
 WORKDIR /app
-COPY package*.json ./
+RUN npm install express cors docx
-RUN npm ci --omit=dev
 COPY server.js ./
 COPY --from=build /app/build ./build