feat(dashboard): per-metric sparklines in the Host Agent — Resources widget

Operator ask: show the graphs next to their fields in the fleet widget, like the
host page's AGENT panel. Each row now renders cpu/mem/disk/load as a value with a
trend sparkline beneath it (1h window), instead of bare numbers.

- _fleet_rows fetches a per-host recent series (cpu/mem/load host-level, disk from
  the root mount) in one 1h query and attaches a sparkline per metric to each row.
- widget_table.html lays out a metric cell (label + threshold-coloured value +
  sparkline) per field, mirroring panel.html. Threshold colour is computed in the
  loop and passed into the cell macro (keeps Jinja macro scope clean).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plugins/host_agent/routes.py

@@ -349,6 +349,39 @@ async def _fleet_rows(session) -> list[dict]:
             continue
         latest.setdefault(row.resource_name, {})[row.metric_name] = row.value
 
+    # Per-host recent series for the inline sparklines (cpu/mem/load host-level,
+    # disk from the root mount), so each metric shows its trend beside the value —
+    # the host-panel at-a-glance, on the fleet widget. 1h window keeps it cheap.
+    host_names = [h.name for h in hosts.values()]
+    spark_series: dict[str, dict[str, list]] = {
+        n: {"cpu": [], "mem": [], "disk": [], "load": []} for n in host_names
+    }
+    if host_names:
+        since = datetime.now(timezone.utc) - timedelta(hours=1)
+        sp_rows = (await session.execute(
+            select(PluginMetric).where(
+                PluginMetric.source_module == SOURCE_MODULE,
+                PluginMetric.recorded_at >= since,
+                or_(
+                    and_(PluginMetric.resource_name.in_(host_names),
+                         PluginMetric.metric_name.in_(("cpu_pct", "mem_used_pct", "load_1m"))),
+                    and_(PluginMetric.resource_name.in_([n + ":/" for n in host_names]),
+                         PluginMetric.metric_name == "disk_used_pct"),
+                ),
+            ).order_by(PluginMetric.recorded_at)
+        )).scalars().all()
+        for r in sp_rows:
+            if r.resource_name.endswith(":/"):
+                name = r.resource_name[:-2]
+                if name in spark_series:
+                    spark_series[name]["disk"].append(r.value)
+            else:
+                key = {"cpu_pct": "cpu", "mem_used_pct": "mem", "load_1m": "load"}.get(r.metric_name)
+                if key and r.resource_name in spark_series:
+                    spark_series[r.resource_name][key].append(r.value)
+
+    from steward.core.status import sparkline_svg
+
     stale_after = _stale_after_seconds()
     now = datetime.now(timezone.utc)
     rows = []
@@ -359,6 +392,11 @@ async def _fleet_rows(session) -> list[dict]:
         m = latest.get(host.name, {})
         ls = reg.last_seen_at
         stale = ls is None or (now - ls).total_seconds() > stale_after
+        ser = spark_series.get(host.name, {})
+        sparks = {
+            k: (sparkline_svg(v[-60:], width=72, height=16) if len(v) >= 2 else "")
+            for k, v in ser.items()
+        }
         rows.append({
             "host": host,
             "reg": reg,
@@ -371,6 +409,7 @@ async def _fleet_rows(session) -> list[dict]:
             "temp_max": m.get("temp_c_max"),
             "net_rx_bps": m.get("net_rx_bps"),
             "net_tx_bps": m.get("net_tx_bps"),
+            "sparks": sparks,
         })
     rows.sort(key=lambda r: r["host"].name.lower())
     return rows