Fix Prisma engine load on Alpine: install openssl + pin musl-openssl-3.0.x

node:20-alpine ships OpenSSL 3.x and has no libssl.so.1.1. Without the
openssl CLI, Prisma's version detection failed and fell back to the
openssl-1.1.x engine, which then failed to load its shared library and
emitted plain text instead of JSON ("Unexpected token 'E'..."), crashing
`prisma migrate deploy` at container startup.

- Install openssl in the build and runtime stages so detection succeeds
- Pin binaryTargets to linux-musl-openssl-3.0.x so the correct engine is bundled

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Dockerfile

@@ -8,6 +8,8 @@ RUN npm run build
 
 # ── Backend bauen (Express + TS + Prisma) ──
 FROM node:20-alpine AS server-build
+# Prisma braucht OpenSSL zur Erkennung der libssl-Version (sonst Fallback auf 1.1.x -> Engine-Ladefehler)
+RUN apk add --no-cache openssl
 WORKDIR /app/server
 COPY server/package*.json ./
 RUN npm install
@@ -17,6 +19,8 @@ RUN npm run build
 
 # ── Laufzeit-Image ──
 FROM node:20-alpine
+# OpenSSL auch zur Laufzeit für "prisma migrate deploy" nötig
+RUN apk add --no-cache openssl
 WORKDIR /app
 ENV NODE_ENV=production
 COPY --from=server-build /app/server/node_modules ./node_modules