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>

plugins/syslog/mcp_tools.py

@@ -25,6 +25,10 @@ async def list_syslog_sources(state: str = "") -> dict:
       "offered" (sending but not added: counted, not kept), "ignored";
       empty for all.
 
+    A device whose lines reach Steward through Docker's own address (a port
+    published on Swarm's ingress) is told apart by the name its lines carry:
+    `through_docker` is true and `address` is Docker's, shared with the others.
+
     Each gives its address, the host it is shown on, lines received in all
     (`lines_total`) and, for an added source, in the last hour, when it was
     last heard and its newest line. search_syslog searches the kept lines.
@@ -41,6 +45,7 @@ async def list_syslog_sources(state: str = "") -> dict:
         hosts = {h.id: h.name for h in (await db.execute(select(Host))).scalars()}
     return {"sources": [{
         "source_id": s.id, "name": source_name(s), "address": s.address, "state": s.state,
+        "through_docker": bool(s.sender),
         "host_id": s.host_id, "host_name": hosts.get(s.host_id), "calls_itself": s.hostname_seen or None,
         "lines_total": s.lines_total, "lines_last_hour": per_hour.get(s.id, 0) if s.state == "accepted" else None,
         "last_heard": iso(s.last_seen_at), "last_heard_age_s": age_s(s.last_seen_at, now),