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/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"