docs: record real two-machine validation of Phase 6 on the Pi

The full chain — mDNS discovery, signaling negotiation, RTP over
Wi-Fi, software H.264 decode, and fullscreen KMSDRM letterboxed
rendering — is confirmed working on a real two-machine setup
(desktop -> Raspberry Pi Zero 2 W headless receiver). The probe
gradient appeared on the Pi's display.

.agents/MEMORY.md

@@ -65,6 +65,14 @@ loopback; current phase is Phase 7.
   before the fix). Cross-compiling on the dev machine was considered and
   dropped — the on-Pi build works and the toolchain/container effort was
   not needed.
+- **REAL-HARDWARE VALIDATION (desktop → Pi Zero 2 W over Wi-Fi)**: the full
+  chain works on two machines: mDNS discovery → signaling negotiation →
+  RTP over Wi-Fi → software H.264 decode → fullscreen KMSDRM letterboxed
+  rendering on the Pi's display. Two transport lessons from that network:
+  the LAN's 6to4 (2002::) addresses are unreachable between peers —
+  senders now try all discovered addresses in reachability order (private
+  IPv4 first; build/pi_probe.cpp in the build dir is the probe that
+  validated this end-to-end against the real Pi).
 
 - **Phase 5 (local UDP sender→receiver loopback) is implemented**:
   - `UdpRtpTransport` (src/network/udp_transport.cpp): raw POSIX sockets,