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>

plugins/snmp/models.py

@@ -46,3 +46,6 @@ class SnmpDevice(Base):
     tables: Mapped[dict] = mapped_column(JSON, nullable=False, default=dict)
     tables_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
     texts: Mapped[dict] = mapped_column(JSON, nullable=False, default=dict)
+    # The name the device reports (sysName), asked with every poll: how a
+    # device whose syslog comes through Docker's address is found (#6096).
+    sys_name: Mapped[str] = mapped_column(String(255), nullable=False, default="")