Per the user's decision, BalDav pulls .rd5 tiles from their own mirror instead
of brouter.de directly. downloadTile now tries, in order: LAN
http://192.168.1.1:88/brouter/segments4, WAN http://77.66.192.45:8088/... (via
the router port-forward), then brouter.de as a last resort; a base that 4xx's
or fails is skipped. The mirror is the Keenetic's existing uhttpd (:88, docroot
/opt/share/www) serving /opt/share/www/brouter/ off USB — always on.
Verified on device: the phone downloads a tile from the LAN mirror in <2s and
routes on it. Routing stays local (embedded engine); the PC RouteServer +
systemd unit are the user's separate remote endpoint, not used by BalDav.
Debug builds allow cleartext; release needs a network-security-config for the
mirror hosts. WAN port-forwards on the router are outward-facing (added
separately with confirmation).