chore(deps): pin dependencies

backend/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:24.04 AS base
+FROM ubuntu:24.04@sha256:99c35190e22d294cdace2783ac55effc69d32896daaa265f0bbedbcde4fbe3e5 AS base
 SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 RUN groupadd -r appuser && useradd -r -g appuser -s /bin/false appuser
 WORKDIR /app
@@ -52,7 +52,7 @@ RUN mkdir -p /tmp/prod/app/node_modules/.prisma/client \
     chmod 777 /tmp/prod/app/prisma/data && \
     chmod 666 /tmp/prod/app/prisma/data/deploy.db
 
-FROM gcr.io/distroless/cc-debian12:nonroot AS production
+FROM gcr.io/distroless/cc-debian12:nonroot@sha256:fe61a509ada74719dbab670d4c0d127bd9b2e0114d18d4bb0a3b25c5d6695a49 AS production
 WORKDIR /
 COPY --from=build /tmp/prod/node_modules /node_modules
 COPY --from=build /tmp/prod/app /app