wiki: Dingtian relay decision, HTTP-over-MQTT, unmanned direction

- dingtian-relay: relay+input controller (4ch on hand). Inputs are decoupled
  from relays (configurable via input_link_relay) — solves the
  access-controller-button-flow blocker the UHPPOTE couldn't. Full protocol from
  the SDK (UDP string control :60001, `00` status parse, input_link_url push,
  multicast discovery). Driver + hardware test still to build.
- dingtian-vs-mqtt: use direct HTTP/UDP now; MQTT skipped (broker = extra infra
  + failure mode + overkill at one-host/few-devices scale) but kept for later
  multi-lane scale.
- autonomous-direction: record the roadmap to fully unmanned (no booth) and how
  it reshapes the threat model (operator-fraud -> unattended-machine threats),
  makes host-in-the-loop entry mandatory, and raises fail-state stakes.
- threat-model: note the unmanned shift. index + log.

gitignore the vendor SDK (dingtian/, 71MB of binaries/examples) — reference
only, protocol captured in the wiki.

.gitignore

@@ -17,4 +17,6 @@ dist/
 *:Zone.Identifier
 .playwright-mcp/
 # stray hardware/UI test screenshots
-/*.png
+/*.png
+# Vendor device SDKs (reference only — protocol captured in wiki, not committed)
+/dingtian/