fix(frontend): copy .npmrc into docker builds, use glibc build stage

npm ci in the images ran without frontend/.npmrc, so the eslint 9/10 peer
conflict aborted it (legacy-peer-deps=true lives in .npmrc). The release
build stage also used alpine/musl, where npm ci skipped the rolldown
native bindings and vite build failed; build on glibc like dev instead.

frontend/Dockerfile.prod

@@ -1,6 +1,6 @@
-FROM node:22-alpine AS build
+FROM node:22 AS build
 WORKDIR /src
-COPY frontend/package.json frontend/package-lock.json ./
+COPY frontend/package.json frontend/package-lock.json frontend/.npmrc ./
 RUN npm ci
 COPY frontend/ ./
 RUN npm run build