feat(open-notebook): Quadlet pair — app + SurrealDB on a private bridge

Two containers, because that is what upstream runs (docker-compose.yml:6,13):
the app image under supervisord, plus SurrealDB. The `v1-latest-single` tag is
not in play — it bundles its own database, is deprecated upstream, and would
give the host a second hidden DB.

Both images are digest-pinned with Pull=never and a documented one-time pull,
the frank-dragoon posture: a Quadlet on :latest re-resolves on the first restart
after an unrelated daemon-reload, and the failure is silent.

Port map paid for by what is already on the host: seerr holds 127.0.0.1:5055
(since 2026-10-14, live `ss -ltn` agrees), so the API leaves on 5056 and the env
file has to set API_URL to match, because the frontend derives the API URL from
the window origin when it is unset. 8502 publishes on 0.0.0.0 — the service
carries its own password and the episode-audio route is unauthenticated. 8000 is
published nowhere, where upstream exposes it on loopback with root credentials.

The app joins dankclaw_default first and the private systemd-open-notebook
second: it reaches the published fleet endpoints through the former
(host.containers.internal, the arrangement Prometheus is proven against) and
finds its database by container name through the latter. Generated --network
flags keep file order, so the tunable file is listed before the host secret file
in both units — podman applies last-match-wins.

No UserMapping: the app runs as root in its namespace (no USER in the Dockerfile)
and writes only paths owned by that root. Exec= carries no database credential —
`exec start --user --pass` puts it in world-readable argv; the image's own
entrypoint passes it on stdin, so only the container env holds it.

dankclaw/open-notebook/quadlet/open-notebook.network

@@ -0,0 +1,34 @@
+# Quadlet network: private bridge for the open-notebook pair (rootless).
+#
+# Install path on dankclaw: ~/.config/containers/systemd/open-notebook.network
+# Unit name: open-notebook-network.service (podman network name:
+# systemd-open-notebook — quadlet prefixes "systemd-", so probe the runtime
+# name, never the filename; see [[Container Network Namespaces]]).
+#
+# WHY A PRIVATE BRIDGE. The app reaches its database by container name
+# (SURREAL_URL=ws://open-notebook-surrealdb:8000/rpc), and container DNS names
+# resolve only on the network that owns them. Putting SurrealDB here instead of
+# on dankclaw_default keeps the datastore reachable ONLY to the container that
+# owns it: 8000 is not published (an unpublished port is refused outright from
+# every other namespace anyway), and nothing else on the fleet-wide network can
+# dial it with the root credentials. Same reasoning as the gitea and authentik
+# database pairs.
+#
+# Kernel bridge, not slirp4netns: the 2026-08-22 open-webui incident (a dead
+# per-container userspace helper left a container that accepted TCP and reset
+# every request for two days, logging nothing). A bridge has no such helper.
+#
+# Subnet registry on dankclaw (rootless):
+#   10.88.0.0/16  default "podman" bridge
+#   10.89.0.0/24  gitea (systemd-gitea)
+#   10.89.1.0/24  compose stack (dankclaw_default)
+#   10.89.2.0/24  searxng (systemd-searxng)
+#   10.89.3.0/24  open-webui (systemd-open-webui)
+#   10.89.4.0/24  open-notebook (systemd-open-notebook)  <- this file
+# Pinned so the container IPs stay deterministic across reboots, like the
+# other pinned nets; 10.89.4.0/24 was the next unclaimed /24 in this registry.
+
+[Network]
+Driver=bridge
+Subnet=10.89.4.0/24
+Gateway=10.89.4.1