fix: set app user shell to /bin/bash so VSCode terminals work

baseimage-gui creates the app user (UID 1000) at runtime with
shell=/sbin/nologin and home=/dev/null. VSCode tries to spawn the
user's login shell for terminals, which fails with exit code 1.

Adds a cont-init script that runs as root after baseimage-gui's
adduser step and corrects both the shell and home directory.

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

Dockerfile

@@ -58,9 +58,11 @@ RUN groupadd -g 1000 user && \
 RUN mkdir -p /workspace && \
     chown -R user:user /workspace
 
-# Copy startup script
+# Copy startup scripts
 COPY --chmod=755 scripts/startapp.sh /startapp.sh
 COPY --chmod=755 scripts/init-repo.sh /usr/local/bin/init-repo
+# Fix app user shell after baseimage-gui creates it at runtime
+COPY --chmod=755 scripts/cont-init-user.sh /etc/cont-init.d/20-fix-user-shell.sh
 
 # Set working directory
 WORKDIR /workspace

scripts/cont-init-user.sh

@@ -0,0 +1,6 @@
+#!/bin/sh
+# Fix the app user (UID 1000) created by baseimage-gui at runtime.
+# baseimage-gui sets shell=/sbin/nologin and home=/dev/null, which
+# prevents VSCode from opening terminals.
+usermod -s /bin/bash app
+usermod -d /home/user app