Dashboard: rebuild into an operator cockpit (0.38.0)

Replace the analytics-style dashboard (stack-health funnel, uptime %,
operations/day grid, AI pill) with an attention-driven fleet cockpit:

- New /api/dashboard/fleet endpoint: server-side fan-out across the local
  host and every agent into one payload — a prioritized "needs attention"
  list, headline KPIs, an honest stack-status breakdown and a per-host
  resource rollup. Each agent uses its own DB session so the fan-out is
  concurrency-safe; failures degrade to "offline" instead of stalling.
- New frontend: AttentionStrip, FleetKpiRow, StackStatusBar and
  HostResourceTable; Dashboard.tsx rewritten around them.
- Remove the funnel/summary endpoints, the uptime sampler loop and the
  ops-activity machinery; delete the now-unused chart components.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/dashboard/FleetKpiRow.tsx

@@ -0,0 +1,96 @@
+import { Link } from "react-router-dom";
+import { Server, Boxes, Container, HeartPulse, ArrowUpCircle, Archive } from "lucide-react";
+import type { FleetKpis } from "@/api/dashboard";
+import { cn } from "@/lib/utils";
+
+type Tone = "default" | "warn" | "error";
+
+function Kpi({
+  icon,
+  label,
+  value,
+  sub,
+  tone = "default",
+  to,
+}: {
+  icon: React.ReactNode;
+  label: string;
+  value: React.ReactNode;
+  sub?: string;
+  tone?: Tone;
+  to?: string;
+}) {
+  const toneText =
+    tone === "error"
+      ? "text-red-600 dark:text-red-400"
+      : tone === "warn"
+        ? "text-sp-amber"
+        : "text-sp-text-1";
+  const inner = (
+    <div className="sp-card flex h-full flex-col gap-1 p-4">
+      <div className="flex items-center gap-1.5 text-sp-text-3">
+        <span className="[&>svg]:h-3.5 [&>svg]:w-3.5">{icon}</span>
+        <span className="sp-label">{label}</span>
+      </div>
+      <p className={cn("sp-display text-3xl leading-none", toneText)}>{value}</p>
+      {sub && <p className="text-xs text-sp-text-3">{sub}</p>}
+    </div>
+  );
+  return to ? (
+    <Link to={to} className="block transition-transform hover:-translate-y-0.5">
+      {inner}
+    </Link>
+  ) : (
+    inner
+  );
+}
+
+export function FleetKpiRow({ kpis }: { kpis: FleetKpis }) {
+  return (
+    <div className="grid grid-cols-2 gap-3 sm:grid-cols-3 lg:grid-cols-6">
+      <Kpi
+        icon={<Server />}
+        label="Hosts"
+        value={`${kpis.hosts_online}/${kpis.hosts_total}`}
+        sub="online"
+        tone={kpis.hosts_online < kpis.hosts_total ? "error" : "default"}
+      />
+      <Kpi
+        icon={<Boxes />}
+        label="Stacks"
+        value={`${kpis.stacks_running}/${kpis.stacks_total}`}
+        sub={kpis.stacks_partial > 0 ? `${kpis.stacks_partial} partial` : "running"}
+        tone={kpis.stacks_partial > 0 ? "warn" : "default"}
+      />
+      <Kpi
+        icon={<Container />}
+        label="Containers"
+        value={`${kpis.containers_running}/${kpis.containers_total}`}
+        sub="running"
+      />
+      <Kpi
+        icon={<HeartPulse />}
+        label="Unhealthy"
+        value={kpis.unhealthy}
+        sub={kpis.unhealthy > 0 ? "need a look" : "all healthy"}
+        tone={kpis.unhealthy > 0 ? "error" : "default"}
+      />
+      <Kpi
+        icon={<ArrowUpCircle />}
+        label="Updates"
+        value={kpis.updates_available}
+        sub={kpis.updates_available > 0 ? "available" : "up to date"}
+        tone={kpis.updates_available > 0 ? "warn" : "default"}
+        to={kpis.updates_available > 0 ? "/images" : undefined}
+      />
+      <Kpi
+        icon={<Archive />}
+        label="Backups"
+        value={kpis.backups_failing > 0 ? kpis.backups_failing : "OK"}
+        sub={kpis.backups_failing > 0 ? "failing/overdue" : "on schedule"}
+        tone={kpis.backups_failing > 0 ? "error" : "default"}
+        to={kpis.backups_failing > 0 ? "/settings" : undefined}
+      />
+    </div>
+  );
+}