feat(syslog): devices through Swarm's ingress told apart by name; the send-to address is a setting (#6096)

Through ingress every device arrives from Docker's own address, so a
source there is keyed by the hostname its lines carry (new column
sender, unique with address). The set-up help no longer guesses the
address from the web hostname: it shows the plugin's send_to setting,
covers ingress and host mode, ASUSTOR ADM, and both syslog formats.

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

tests/integration/test_syslog.py

@@ -71,6 +71,41 @@ def test_an_unknown_sender_is_offered_and_an_added_one_kept(app):
     asyncio.run(go())
 
 
+def test_devices_through_dockers_address_are_told_apart_by_name(app, monkeypatch):
+    """Through Swarm's ingress every device arrives from Docker's address
+    (#6096): there each name its lines carry is its own source."""
+    from sqlalchemy import delete, select
+
+    SyslogSource = _mod("models").SyslogSource
+    receiver = _mod("receiver")
+    parse = _mod("parse").parse
+    monkeypatch.setattr(receiver, "on_own_network", lambda address: address.startswith("10.0.0."))
+    now = datetime(2026, 10, 19, 3, 0, tzinfo=timezone.utc)
+
+    def line(address, host, text):
+        return receiver.Received(now, address, parse(f"<14>Oct 19 01:12:03 {host} kernel: {text}"))
+
+    async def go():
+        async with app.db_sessionmaker() as s:
+            async with s.begin():
+                await s.execute(delete(SyslogSource))
+                await receiver.store_lines(s, [line("10.0.0.2", "SynNAS", "a"), line("10.0.0.2", "AsusNAS", "b"),
+                                               line("10.0.0.2", "SynNAS", "c")])
+        async with app.db_sessionmaker() as s:
+            async with s.begin():
+                await receiver.store_lines(s, [line("10.0.0.2", "AsusNAS", "d"), line("10.9.0.1", "renamed", "e")])
+        async with app.db_sessionmaker() as s:
+            rows = (await s.execute(select(SyslogSource))).scalars().all()
+            got = sorted((r.address, r.sender, r.lines_total, r.last_line) for r in rows)
+            assert got == [("10.0.0.2", "AsusNAS", 2, "d"), ("10.0.0.2", "SynNAS", 2, "c"),
+                           ("10.9.0.1", "", 1, "e")]
+        async with app.db_sessionmaker() as s:
+            async with s.begin():
+                await s.execute(delete(SyslogSource))
+
+    asyncio.run(go())
+
+
 def test_the_ring_keeps_each_source_within_its_window_and_cap(app):
     from sqlalchemy import delete, select