feat(web): add Fleet dashboard view for cross-instance observability

Adds a new /fleet route that shows a fleet-wide overview of all
configured Honcho instances. Each row renders per-instance metrics
(workspace count, total conclusions, queue activity, last seen, health)
by fanning out scoped fetches via createScopedClient, and aggregates
into top-level metric cards.

Reuses the Phase 2 scoped-client pattern. Extends compareQueries.ts
with useScopedQueueStatus and useScopedConclusionsCount, plus option
builders so useQueries can fan out per-workspace requests inside
FleetRow without duplicating query logic.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/web/src/components/layout/Sidebar.tsx

@@ -15,6 +15,7 @@ import {
 	MessageSquare,
 	Moon,
 	MoonStar,
+	Network,
 	Settings,
 	Sun,
 	Users,
@@ -31,6 +32,7 @@ import { COLOR } from "@/lib/constants";
 
 const TOP_NAV = [
 	{ to: "/" as const, label: "Dashboard", icon: LayoutDashboard, exact: true },
+	{ to: "/fleet" as const, label: "Fleet", icon: Network, exact: false },
 	{ to: "/workspaces" as const, label: "Workspaces", icon: Boxes, exact: false },
 	{ to: "/seed-kits" as const, label: "Seed Kits", icon: Layers, exact: false },
 	{ to: "/settings" as const, label: "Settings", icon: Settings, exact: false },