Fix backend image build: use hoisted node_modules in the Docker context

The previous Dockerfile assumed Prisma's generated client landed at
tehriehlbudget-backend/node_modules/.prisma/client/, but pnpm's default
isolated layout writes it inside node_modules/.pnpm/@prisma+client@.../
node_modules/, which doesn't survive a multi-stage COPY. The build
failed at the runtime stage trying to copy a path that didn't exist.

Switch the image to hoisted (flat) node_modules via a build-context-only
.npmrc so prisma generate writes to predictable /repo/node_modules/
{@prisma,.prisma}/ paths. Local dev keeps the isolated layout — the
.npmrc lives only inside the docker build context, not on disk.

The runtime stage now copies node_modules from the workspace root
(where hoisted deps live), then overlays the generated Prisma client
from the build stage (since the prod-deps stage strips the prisma CLI).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tehriehlbudget-backend/Dockerfile

@@ -5,6 +5,13 @@ FROM node:${NODE_VERSION}-alpine AS deps
 RUN apk add --no-cache libc6-compat openssl
 RUN corepack enable && corepack prepare pnpm@9 --activate
 WORKDIR /repo
+# Force a hoisted (flat) node_modules layout for the image. The default pnpm
+# isolated layout puts dependencies inside node_modules/.pnpm/<pkg>@<ver>/
+# which makes `prisma generate`'s output (node_modules/.prisma/client/) live
+# in a path that doesn't survive a multi-stage COPY. Hoisted gives us
+# predictable /repo/node_modules/{@prisma,.prisma}/ paths. Local dev is
+# unaffected — this .npmrc only exists inside the build context.
+RUN echo "node-linker=hoisted" > /repo/.npmrc
 COPY pnpm-workspace.yaml pnpm-lock.yaml package.json ./
 COPY tehriehlbudget-backend/package.json  tehriehlbudget-backend/
 COPY tehriehlbudget-frontend/package.json tehriehlbudget-frontend/
@@ -30,11 +37,12 @@ ENV NODE_ENV=production
 COPY --from=build     --chown=nodeapp:nodeapp /repo/tehriehlbudget-backend/dist          ./dist
 COPY --from=build     --chown=nodeapp:nodeapp /repo/tehriehlbudget-backend/prisma        ./prisma
 COPY --from=build     --chown=nodeapp:nodeapp /repo/tehriehlbudget-backend/package.json  ./package.json
-COPY --from=prod-deps --chown=nodeapp:nodeapp /repo/tehriehlbudget-backend/node_modules  ./node_modules
-# Overlay generated Prisma client from the build stage (the prod-deps stage
-# pruned the `prisma` CLI devDep, which removes the client during install).
-COPY --from=build     --chown=nodeapp:nodeapp /repo/tehriehlbudget-backend/node_modules/.prisma  ./node_modules/.prisma
-COPY --from=build     --chown=nodeapp:nodeapp /repo/tehriehlbudget-backend/node_modules/@prisma  ./node_modules/@prisma
+# With hoisted linker, all deps live at the workspace-root node_modules.
+COPY --from=prod-deps --chown=nodeapp:nodeapp /repo/node_modules  ./node_modules
+# Overlay the generated Prisma client from the build stage. The prod-deps
+# stage doesn't have the `prisma` CLI (devDep) so it can't generate.
+COPY --from=build     --chown=nodeapp:nodeapp /repo/node_modules/.prisma  ./node_modules/.prisma
+COPY --from=build     --chown=nodeapp:nodeapp /repo/node_modules/@prisma  ./node_modules/@prisma
 USER nodeapp
 EXPOSE 3000
 ENTRYPOINT ["/sbin/tini", "--"]