Add auto-expand service in pull-image.sh

Create a systemd oneshot service that expands the rootfs on first boot
after flashing. The service self-destructs after running.

This ensures release images fill the SD card while keeping the
download size small (16GB shrunk image).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

rpi/pull-image.sh

@@ -123,6 +123,37 @@ else
     echo -e "${GREEN}  Rootfs already ~16GB${NC}"
 fi
 
+# ============================================================================
+# Re-enable auto-expand for release image
+# ============================================================================
+echo
+echo -e "${YELLOW}Re-enabling auto-expand for release...${NC}"
+TEMP_ROOT=$(mktemp -d)
+mount "$ROOT_PART" "$TEMP_ROOT"
+
+# Create the resize service that runs on first boot
+cat > "$TEMP_ROOT/etc/systemd/system/rpi-resizerootfs.service" <<'RESIZE_EOF'
+[Unit]
+Description=Resize root filesystem to fill SD card
+After=local-fs.target
+
+[Service]
+Type=oneshot
+ExecStart=/bin/bash -c 'resize2fs $(findmnt -n -o SOURCE /) && systemctl disable rpi-resizerootfs.service && rm -f /etc/systemd/system/rpi-resizerootfs.service'
+ExecStartPost=/bin/systemctl daemon-reload
+
+[Install]
+WantedBy=multi-user.target
+RESIZE_EOF
+
+# Enable the service
+mkdir -p "$TEMP_ROOT/etc/systemd/system/multi-user.target.wants"
+ln -sf /etc/systemd/system/rpi-resizerootfs.service "$TEMP_ROOT/etc/systemd/system/multi-user.target.wants/rpi-resizerootfs.service"
+
+umount "$TEMP_ROOT"
+rmdir "$TEMP_ROOT"
+echo -e "${GREEN}  Auto-expand service installed${NC}"
+
 # ============================================================================
 # Pull image
 # ============================================================================