- feat: full TAK Route support (multiple <link> elements + link_attr); Detail
  now distinguishes route links (point attr) from shape links (727041b).
- fix: Event.ToXML() emits the <contact> endpoint attribute (INFR-207 / INFR-206)
  — the TAK server keys callsign->connection routing off endpoint, so dropping it
  broke inbound DM routing to a self-SA presence.

Verified: full suite (cgo libxml2 validator) + race + fuzz green; endpoint
round-trip guard + route tests pass; live e2e — takconnector built on this tag
registers callsign NERVA on the TAK server (Set client ... to NERVA).