fix(docker): resolve user creation issues in Dockerfile

- Move WORKDIR after user creation to prevent home directory ownership issues
- Properly set environment variables for UID, GID, HOME, and USER in each stage
- Reorganize Dockerfile to ensure home directory is created after user setup
- Fix interactive prompts during adduser by ensuring proper directory ownership

Author: gustavovalverde

docker/Dockerfile

@@ -60,14 +60,6 @@ ARG SHORT_SHA
 # https://github.com/ZcashFoundation/zebra/blob/9ebd56092bcdfc1a09062e15a0574c94af37f389/zebrad/src/application.rs#L179-L182
 ENV SHORT_SHA=${SHORT_SHA:-}
 
-# Set the working directory for the build.
-ARG HOME
-WORKDIR ${HOME}
-ENV HOME=${HOME}
-ENV CARGO_HOME="${HOME}/.cargo/"
-
-ENV USER=${USER}
-
 # This stage builds tests without running them.
 #
 # We also download needed dependencies for tests to work, from other images.
@@ -84,15 +76,22 @@ ENV ZEBRA_SKIP_IPV6_TESTS=${ZEBRA_SKIP_IPV6_TESTS:-1}
 # This environment setup is almost identical to the `runtime` target so that the
 # `tests` target differs minimally. In fact, a subset of this setup is used for
 # the `runtime` target.
-
 ARG UID
+ENV UID=${UID}
 ARG GID
+ENV GID=${GID}
 ARG HOME
+ENV HOME=${HOME}
 ARG USER
+ENV USER=${USER}
 
 RUN addgroup --gid ${GID} ${USER} && \
     adduser --gid ${GID} --uid ${UID} --home ${HOME} ${USER}
 
+# Set the working directory for the build.
+WORKDIR ${HOME}
+ENV CARGO_HOME="${HOME}/.cargo/"
+
 # Build Zebra test binaries, but don't run them
 
 # Leverage a cache mount to /usr/local/cargo/registry/
@@ -193,13 +192,7 @@ ARG FEATURES
 ENV FEATURES=${FEATURES}
 
 # Create a non-privileged system user for running `zebrad`.
-ARG USER
-ENV USER=${USER}
-
-# System users have no home dirs, but we set one for users' convenience.
-ARG HOME
-WORKDIR ${HOME}
-
+#
 # We use a high UID/GID (10001) to avoid overlap with host system users.
 # This reduces the risk of container user namespace conflicts with host accounts,
 # which could potentially lead to privilege escalation if a container escape occurs.
@@ -216,10 +209,17 @@ ARG UID
 ENV UID=${UID}
 ARG GID
 ENV GID=${GID}
+ARG HOME
+ENV HOME=${HOME}
+ARG USER
+ENV USER=${USER}
 
 RUN addgroup --gid ${GID} ${USER} && \
     adduser --gid ${GID} --uid ${UID} --home ${HOME} ${USER}
 
+# System users have no home dirs, but we set one for users' convenience.
+WORKDIR ${HOME}
+
 # We set the default locations of the conf and cache dirs according to the XDG
 # spec: https://specifications.freedesktop.org/basedir-spec/latest/