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/routes/fleet.tsx

@@ -0,0 +1,6 @@
+import { createFileRoute } from "@tanstack/react-router";
+import { FleetDashboard } from "@/components/fleet/FleetDashboard";
+
+export const Route = createFileRoute("/fleet")({
+	component: FleetDashboard,
+});