fix(docker): bake the pip image's prisma engines at a world-readable path (#35976)

The build_from_pip image ran a bare `prisma generate`, so prisma recorded
absolute engine paths under $HOME/.cache, which is /root/.cache in that
build. /root is mode 0700 on python:3.13-slim, so any runtime uid other
than 0 gets EACCES just traversing it and the proxy dies during prisma
client initialisation. That is exactly the shape a securityContext with
runAsUser produces.

Generate under a fixed /opt/prisma and chmod it a+rX, matching what the
shipped images already do, and pin PRISMA_BINARY_CACHE_DIR at runtime so
the client resolves the baked engines instead of looking under $HOME. A
build-time assertion fails the build if any recorded engine path lands
outside the pinned prefix, since the original breakage was silent at
build time and only surfaced as a runtime crash for non-root users.

docker/build_from_pip/Dockerfile.build_from_pip

@@ -47,7 +47,13 @@ RUN uv venv --python python && \
       "prisma==0.11.0" \
       "openai==2.24.0"
 
-RUN prisma generate --schema=./schema.prisma
+RUN HOME=/opt/prisma XDG_CACHE_HOME=/opt/prisma/.cache PRISMA_BINARY_CACHE_DIR=/opt/prisma/binaries \
+    npm_config_cache=/root/.npm \
+    prisma generate --schema=./schema.prisma && \
+    chmod -R a+rX /opt/prisma && \
+    python -c "import sys; from prisma.client import BINARY_PATHS; bad = sorted(p for group in BINARY_PATHS.model_dump().values() for p in group.values() if not p.startswith('/opt/prisma/')); sys.exit('prisma engines baked outside /opt/prisma: %r' % bad) if bad else None"
+
+ENV PRISMA_BINARY_CACHE_DIR=/opt/prisma/binaries
 
 EXPOSE 4000/tcp