chore(docker/backend): set HOME env var to /fradrive for stack root

.gitignore

@@ -9,6 +9,7 @@ bin/
 *.sqlite3-wal
 .hsenv*
 cabal-dev/
+.stack/
 .stack-work/
 yesod-devel/
 .cabal-sandbox

docker/backend/Dockerfile

@@ -8,5 +8,8 @@ RUN apt-get -y install libghc-zlib-dev libpq-dev
 
 WORKDIR /fradrive
 
+ENV HOME=/fradrive
+# ENV STACK_ROOT=/fradrive/.stack
+
 ENV FRADRIVE_MAKE_TARGET=backend-build
 ENTRYPOINT make -- ${FRADRIVE_MAKE_TARGET}