Bring up the USB gadget link (package 0b, Pi side and talos side)

The Pi presents NCM Ethernet and ACM serial from a configfs gadget, started by
robot-usb-gadget.service before networking. usb0 gets 10.55.0.2/30 with no
gateway through netplan, matched by interface name: a MAC match turns into
PermanentMACAddress= in networkd, which a gadget interface does not have, so it
stayed unmanaged. talos reaches the Pi at 10.55.0.2 (ping ~2.4 ms, SSH works)
through a NetworkManager profile, host/omarchy/robot-usb-link.sh, matched by the
gadget's fixed host MAC.

Also clamp the face's tunable parameters (focus sets a blur radius, persistence
divides) and fps, after a review flagged unvalidated node parameters.

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

pi/robot-usb-gadget.service

@@ -0,0 +1,14 @@
+[Unit]
+Description=Robot USB gadget (NCM Ethernet + ACM serial)
+After=sys-kernel-config.mount systemd-modules-load.service
+Before=network-pre.target
+Wants=network-pre.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/usr/local/sbin/robot-usb-gadget start
+ExecStop=/usr/local/sbin/robot-usb-gadget stop
+
+[Install]
+WantedBy=multi-user.target