feat(syslog): set-up help on the page, port 5514 published, Docker-hidden senders called out (#6003)

The Syslog page says where to send (this server, its port and protocols) and
where the setting is on Synology, QNAP, TrueNAS, OpenWrt, UniFi and rsyslog,
open until a device sends. A sender whose address is on Steward's own
container network (Swarm ingress publishing hides the real sender) is
flagged, with the host-mode ports to publish instead. compose files and the
Dockerfile publish 5514/udp and /tcp; docs/plugins/syslog.md describes the
plugin and the deploy.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/plugins/syslog/test_syslog_page.py

@@ -27,7 +27,7 @@ async def _render(app, role, **ctx):
     from quart import session
     ctx = {"listener": _listener(), "sources": [], "offered": [], "ignored": [],
            "hosts": [NS(id="h1", name="SynNAS", address="192.168.0.7")],
-           "now": datetime.now(timezone.utc), **ctx}
+           "server": "steward.lan", "now": datetime.now(timezone.utc), **ctx}
     async with app.test_request_context("/plugins/syslog/"):
         session["user_role"] = role
         page = await render_plugin_template(app, "syslog", "syslog/index.html", **ctx)
@@ -62,6 +62,23 @@ async def test_a_port_it_cannot_open_is_said(app):
     assert "No sources yet." in page
 
 
+async def test_setup_help_names_this_server_and_opens_until_a_device_sends(app):
+    page = await _render(app, "viewer")
+    assert '<details class="card" id="syslog-setup" open>' in page
+    assert "send to <span class=\"mono\">steward.lan</span>, port <span class=\"mono\">5514</span>, UDP or TCP" in page
+    assert "*.* @@steward.lan:5514" in page and "mode: host" in page
+    added = await _render(app, "viewer", sources=[_source("SynNAS", "accepted")])
+    assert '<details class="card" id="syslog-setup">' in added                 # closed once one sends
+
+
+async def test_a_sender_on_dockers_own_network_is_called_out(app):
+    hidden = {**_source("ingress", "offered"), "address": "10.0.0.2", "docker_address": True}
+    page = await _render(app, "admin", offered=[hidden, {**hidden, "id": "id-2"}])
+    assert "10.0.0.2 is on Steward's own container network" in page
+    assert page.count("Docker's address, not the device's") == 2
+    assert "own container network" not in await _render(app, "admin", offered=[_source("synnas", "offered")])
+
+
 async def test_the_edit_page_has_its_trail_and_a_remove(app):
     from quart import session
     source = NS(id="s1", name="SynNAS", hostname_seen="synnas", address="192.168.0.7", host_id=None)