feat(syslog): a device through Docker's address is placed by its name, or a device address set on it (#6096)

The SNMP poll asks each device's sysName in the same GET and keeps it
(snmp_003_sys_name). A syslog source told apart by name finds its own
address from the SNMP device (reported or given name) or host of that
name, so its lines reach the SNMP device's and host's pages again; the
edit page gains Device address, which always wins (syslog_004).

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

docs/plugins/syslog.md

@@ -54,9 +54,15 @@ ports:
 Through ingress every line arrives from Docker's own address on the ingress
 network, so the address no longer tells the devices apart. For such an address
 Steward keys the source by the hostname each line carries instead (#6096): each
-device is its own source, linked to a host by name. A device must put its
-hostname in its lines (NASes and routers do); lines with none at Docker's
-address all fold into one source, and the page says so.
+device is its own source. A device must put its hostname in its lines (NASes
+and routers do); lines with none at Docker's address all fold into one source,
+and the page says so.
+
+Such a source's own address, which places its lines on its SNMP device's and
+host's pages (chart marks, the lines around an anomaly), is found by name: the
+SNMP device whose reported name (sysName, asked with every poll) or given name
+matches, else the host of that name. Where nothing matches, set **Device
+address** on the source's edit page; a value set there always wins.
 
 **Host mode** keeps each device's own address, but only the node running the
 task answers, so devices must be pointed at that node: