fix: basicauth double-prefix render; open-webui off slirp4netns

basicauth (2026-08-22 incident):
- the Caddyfile template carried its own $2a$14$ prefix and deploy.sh
  substituted the full hash (prefix included), rendering an invalid
  double-prefixed hash. Every basicauth vhost rejected every password
  with 401 and Caddy logged nothing.
- template is now a bare REPLACE_WITH_HASH token; tests pin the render
  contract (no prefix in template; rendered line is exactly 'dank <hash>').

open-webui (2026-08-22 incident):
- its slirp4netns helper process died, leaving the container running
  with only 'lo' in its netns: port 3005 accepted TCP and reset every
  request, so chat served empty responses for ~2 days, unlogged.
- move to a pinned bridge network (systemd-open-webui, 10.89.3.0/24,
  gw 10.89.3.1) — no per-container helper to die.
- LLM endpoint reached via the gateway (host.containers.internal is
  slirp-only): OPENAI_API_BASE_URL=http://10.89.3.1:52625.
- add a quadlet healthcheck: /health (app) + non-loopback interface
  (network liveness; the dead-tap state leaves only 'lo').
- deploy script now copies the .network file too.
- docs updated (OpenWebUI History section, Caddy basic-auth contract).

tests/deployment_flow.bats

@@ -44,4 +44,9 @@ load helpers
     [ -n "$rendered" ]
     [[ "$rendered" == *"${hash}"* ]]
     ! grep -q 'REPLACE_WITH_HASH' <<< "$rendered"
+    # The rendered line must be exactly "dank <hash>". A template that keeps
+    # its own $2a$14$ prefix renders an invalid double-prefixed hash and
+    # every basicauth vhost returns 401 (2026-08-22 incident).
+    grep -qF "dank ${hash}" <<< "$rendered"
+    ! grep -qF '$2a$14$$2a$14$' <<< "$rendered"
 }