fix(deploy): install dev deps in builder so tsc is available, keep production deps in final image

deploy/Dockerfile.backend

@@ -1,8 +1,8 @@
 FROM node:20-alpine AS builder
 WORKDIR /app
 COPY backend/package*.json backend/
-# Use npm ci if a lockfile exists in backend, otherwise fall back to npm install
-RUN sh -c 'if [ -f backend/package-lock.json ] || [ -f backend/npm-shrinkwrap.json ]; then npm ci --prefix backend --production; else npm install --prefix backend --production; fi'
+# Install all dependencies (including dev) in builder so tools like tsc are available for build
+RUN sh -c 'if [ -f backend/package-lock.json ] || [ -f backend/npm-shrinkwrap.json ]; then npm ci --prefix backend; else npm install --prefix backend; fi'
 COPY backend/ backend/
 RUN npm run build --prefix backend