Block all DDS off the Pi and bring up PipeWire behind the firewall

ROS never leaves the robot, by the owner's decision: the firewall drops domain
42's DDS ports on every interface but loopback (usb0 included), discovery is
pinned to LOCALHOST, and hermes_mcp is the only bridge to the outside. PipeWire
1.0.5 runs as hermes's user services with its network server on TCP 4713; the
firewall, loaded at boot before it, is the protection. Verified from talos: 4713
connects over usb0 and times out over Wi-Fi.

CONTEXT.md brought up to date: the face service, gaze, recognition, the firewall,
and what is left.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AFN8nRRCiDiMN7ChBpHJhs

pi/nftables-robot.nft

@@ -1,9 +1,10 @@
 #!/usr/sbin/nft -f
 # The robot's audio (4713), MCP (8765) and face webhook (8766) ports are reachable only over the
 # USB link, and only from the host at 10.55.0.1. Every other interface, Wi-Fi included, is dropped.
-# ROS 2's DDS has no authentication, and /camera/* and /vision/faces carry video and recognised
-# names, so its ports (domain 42: 17900-18149 with Fast DDS's default offsets) are dropped on every
-# interface but usb0 and loopback too.
+# ROS 2 never leaves the robot: its DDS has no authentication, and /camera/* and /vision/faces
+# carry video and recognised names. Domain 42's ports (17900-18149 with Fast DDS's default offsets)
+# are dropped on every interface but loopback, usb0 included. The only way in or out is hermes_mcp,
+# which talks to the ROS graph locally and to the host over MCP.
 # SSH and everything else are left alone: that policy is the owner's call.
 
 table inet robot
@@ -15,6 +16,6 @@ table inet robot {
         iif "lo" accept
         iifname "usb0" ip saddr 10.55.0.1 tcp dport { 4713, 8765, 8766 } accept
         tcp dport { 4713, 8765, 8766 } drop
-        iifname != { "lo", "usb0" } udp dport 17900-18149 drop
+        iifname != "lo" udp dport 17900-18149 drop
     }
 }