Fix and update frontend Dockerfile

- Update node image to node 21
- Copy project.inlang before running npm ci

frontend/Dockerfile

@@ -1,16 +1,17 @@
-FROM node:18-alpine AS builder
+FROM node:21-alpine AS builder
 WORKDIR /app
 
 ARG PUBLIC_BACKEND_API_URL
 ENV PUBLIC_BACKEND_API_URL=$PUBLIC_BACKEND_API_URL
 
 COPY package*.json .
+COPY project.inlang/ .
 RUN npm ci
 COPY . .
 RUN npm run build
 RUN npm prune --production
 
-FROM node:18-alpine
+FROM node:21-alpine
 WORKDIR /app
 COPY --from=builder /app/build build/
 COPY --from=builder /app/node_modules node_modules/