feat(frank-dragoon): put the endpoint on the app bridge so app containers can name it

An endpoint on podman's rootless default (pasta) has no address another
container can use, measured on 2026-10-19 from inside open-notebook:

  - 192.168.0.143:7770            connection refused (pasta forwards the
                                  published port in the host netns; no netavark
                                  DNAT exists for traffic arriving from a
                                  rootless bridge)
  - host.containers.internal:7770 200, but the alias resolves to 169.254.1.2 —
                                  link-local, which open-notebook's URL guard
                                  refuses to store
  - frank-dragoon-halogen:8731    name unknown: different netns
  - --network pasta --network dankclaw_default
                                  "cannot set multiple networks without bridge
                                  network mode" — pasta cannot be added to

So reaching the NPU endpoints from an app container means moving the container
onto dankclaw_default (FRANK_DRAGOON_NETWORK; empty keeps today's shape). This
is not an exposure change: the engine's unauthenticated token port binds the
container's own loopback (/proc/net/tcp: 127.0.0.1:8730 against 0.0.0.0:8731),
so only the API port becomes name-resolvable — the same trust the published
7770 already carries on the LAN. The deployer refuses a network that does not
exist rather than starting a unit that restart-loops on it.

Co-Authored-By: omp <omp@dankclaw>

scripts/frank-dragoon.env

@@ -110,3 +110,12 @@ FRANK_DRAGOON_XRT_DIR=/usr/lib/x86_64-linux-gnu
 # sysfs root the fabric-clock preflight reads (same knob the vendor's
 # halogen-fabric-clock status reads; the seam points it at a fixture).
 FRANK_DRAGOON_SYSFS=/sys
+# Container network. Empty = podman's rootless default (`pasta`): a private
+# netns that nothing else can join — podman refuses a second network while the
+# primary is pasta, the published port is refused from dankclaw_default
+# containers, and host.containers.internal resolves link-local, which
+# open-notebook's URL guard refuses to store. Named = the app bridge, so
+# open-notebook can dial http://frank-dragoon-halogen:8731 for the NPU
+# endpoints. The engine's unauthenticated 8730 stays private either way (it
+# binds the container's own loopback); only the API port becomes name-resolvable.
+FRANK_DRAGOON_NETWORK=dankclaw_default