fix: inject motd build info in genapkovl tmp, not overlay on disk

sed -i on overlay/etc/motd caused git pull conflict on next build.
Now BEE_BUILD_INFO is exported and substituted in $tmp copy only.

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

iso/builder/build-debug.sh

@@ -118,11 +118,10 @@ cp "${NVIDIA_CACHE}/bin/nvidia-smi" "${OVERLAY_DIR}/usr/local/bin/"
 chmod +x "${OVERLAY_DIR}/usr/local/bin/nvidia-smi"
 cp "${NVIDIA_CACHE}/lib/"* "${OVERLAY_DIR}/usr/lib/" 2>/dev/null || true
 
-# --- inject build info into motd ---
+# --- export build info for genapkovl to inject into motd ---
 BUILD_DATE=$(date +%Y-%m-%d)
 GIT_COMMIT=$(git -C "${REPO_ROOT}" rev-parse --short HEAD 2>/dev/null || echo "unknown")
-BUILD_INFO="${BUILD_DATE} git:${GIT_COMMIT} alpine:${ALPINE_VERSION} nvidia:${NVIDIA_DRIVER_VERSION}"
-sed -i "s/%%BUILD_INFO%%/${BUILD_INFO}/" "${OVERLAY_DIR}/etc/motd"
+export BEE_BUILD_INFO="${BUILD_DATE} git:${GIT_COMMIT} alpine:${ALPINE_VERSION} nvidia:${NVIDIA_DRIVER_VERSION}"
 
 # --- build ISO using mkimage ---
 mkdir -p "${DIST_DIR}"

iso/builder/genapkovl-bee_debug.sh

@@ -73,6 +73,7 @@ rc_add bee-audit-debug default
 if [ -d "$OVERLAY/etc" ]; then
     cp -r "$OVERLAY/etc/." "$tmp/etc/"
     chmod +x "$tmp/etc/init.d/"* 2>/dev/null || true
+    [ -n "$BEE_BUILD_INFO" ] && sed -i "s/%%BUILD_INFO%%/${BEE_BUILD_INFO}/" "$tmp/etc/motd" 2>/dev/null || true
 fi
 
 mkdir -p "$tmp/usr"