Fix mkimage git conflict: cd /var/tmp before running mkimage.sh

mkimage.sh calls git internally. Running it from inside /root/bee causes
"outside repository" fatal errors. /var/tmp is outside the git repo.
genapkovl is found via ~/.mkimage/ so no copy to /var/tmp needed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/builder/build.sh

@@ -192,9 +192,11 @@ if [ -d /var/tmp/bee-iso-work ]; then
         -exec rm -rf {} + 2>/dev/null || true
 fi
 
-# mkinitfs/update-kernel use TMPDIR for initramfs build; tmpfs /tmp is only ~1GB.
-# genapkovl-bee.sh is found by mkimage via ~/.mkimage/ (copied above) — no CWD dependency.
+# Run from /var/tmp: mkimage.sh calls git internally; running from inside /root/bee causes
+# "outside repository" errors. /var/tmp is outside the git repo and has enough scratch space.
+# genapkovl-bee.sh is found by mkimage via ~/.mkimage/ — no need to copy it to /var/tmp.
 export TMPDIR=/var/tmp
+cd /var/tmp
 sh /usr/share/aports/scripts/mkimage.sh \
     --tag "v${ALPINE_VERSION}" \
     --outdir "${DIST_DIR}" \