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/models.py

@@ -3,7 +3,8 @@ from __future__ import annotations
 
 from datetime import datetime, timezone
 
-from sqlalchemy import JSON, BigInteger, Boolean, DateTime, ForeignKey, Index, SmallInteger, String, Text
+from sqlalchemy import (JSON, BigInteger, Boolean, DateTime, ForeignKey, Index, SmallInteger, String, Text,
+                        UniqueConstraint)
 from sqlalchemy.orm import Mapped, mapped_column
 
 from steward.core.ids import time_ordered_id
@@ -13,6 +14,10 @@ from steward.models.base import Base
 class SyslogSource(Base):
     """A device that sends syslog to Steward, one row per sending address.
 
+    Through a port Swarm publishes on its ingress (the default), every device
+    arrives from one address of Docker's own; there a row is a device by the
+    name its lines carry, `sender` (#6096). Everywhere else `sender` is "".
+
     A sender Steward hasn't been told about is a row too, `state="offered"`:
     its lines are counted and its newest kept as a sample, so the page can
     offer it ("1,204 lines from 192.168.0.7: add as a source?"), but none is
@@ -20,9 +25,11 @@ class SyslogSource(Base):
     on; `"ignored"` stops the offer and keeps counting.
     """
     __tablename__ = "syslog_sources"
+    __table_args__ = (UniqueConstraint("address", "sender", name="uq_syslog_sources_address_sender"),)
 
     id: Mapped[str] = mapped_column(String(36), primary_key=True, default=time_ordered_id)
-    address: Mapped[str] = mapped_column(String(64), nullable=False, unique=True)
+    address: Mapped[str] = mapped_column(String(64), nullable=False)
+    sender: Mapped[str] = mapped_column(String(255), nullable=False, default="")
     state: Mapped[str] = mapped_column(String(10), nullable=False, default="offered")
     name: Mapped[str] = mapped_column(String(100), nullable=False, default="")
     host_id: Mapped[str | None] = mapped_column(