feat(snmp): surface SNMP device readings on the matching host page

SNMP devices are config-defined by IP/hostname, not Steward Host records, so
they had no presence on a host's page. Map them by address and embed a fragment
(mirrors the Docker per-host fragment).

- _devices_for_host(devices_cfg, address, name): case-insensitive match of a
  device's configured host to the Steward host's address or name (tolerates
  non-dict / host-less entries).
- Route /plugins/snmp/host/<id>: renders the matched device(s) + latest readings,
  or nothing when none map (so hosts without SNMP carry no empty card).
- snmp/host_panel.html: per-device card (name · address · reachability) with a
  readings grid (K/M scaling) and a History link to the full device page.
- hosts/detail.html embeds it after the Docker fragment, gated on snmp enabled.
- Unit test for the matching helper (by address, by name, no-match, blank).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016Jg27rgypiW2efULXJDtMC

plugins/snmp/routes.py

@@ -93,6 +93,48 @@ async def index():
                                  poll_interval=poll_interval)
 
 
+def _devices_for_host(devices_cfg: list, address: str | None, name: str | None) -> list[dict]:
+    """SNMP devices whose configured `host` matches a Steward host's address or
+    name (case-insensitive). SNMP devices are config-defined by IP/hostname, so
+    this is how they map onto a host's page."""
+    keys = {(address or "").strip().lower(), (name or "").strip().lower()}
+    keys.discard("")
+    return [
+        d for d in devices_cfg
+        if isinstance(d, dict) and str(d.get("host", "")).strip().lower() in keys
+    ]
+
+
+@snmp_bp.get("/host/<host_id>")
+@require_role(UserRole.viewer)
+async def host_panel(host_id: str):
+    """Per-host SNMP fragment for the Hosts hub. Surfaces any configured SNMP
+    device that maps to this host (by address or name) with its latest readings.
+    Renders nothing when no device maps, so hosts without SNMP carry no empty card.
+    """
+    from steward.models.hosts import Host
+
+    devices_cfg: list[dict] = current_app.config["PLUGINS"]["snmp"].get("devices", [])
+    async with current_app.db_sessionmaker() as db:
+        host = (await db.execute(
+            select(Host).where(Host.id == host_id))).scalar_one_or_none()
+        if host is None:
+            return ""
+        matched = _devices_for_host(devices_cfg, host.address, host.name)
+        if not matched:
+            return ""
+        names = [d.get("name") or d.get("host", "?") for d in matched]
+        latest = await _latest_readings(db, names)
+
+    devices = [{
+        "name": d.get("name") or d.get("host", "?"),
+        "host": d.get("host", ""),
+        "oids": d.get("oids", []),
+        "readings": latest.get(d.get("name") or d.get("host", "?"), {}),
+    } for d in matched]
+    return await render_template("snmp/host_panel.html", devices=devices)
+
+
 @snmp_bp.get("/widget")
 @require_role(UserRole.viewer)
 async def widget():