Add app shell with left nav; split dashboard into top-level pages

Introduce a Layout shell with a collapsible left sidebar (state persisted
to localStorage) that becomes a hamburger drawer under md. Break the single
Dashboard into routed pages — Overview (summary tiles + node bar), Services,
Scheduled, Programs, Gateway, Mesh — nested under the shared Layout via an
Outlet. Centralize useEventStream in Layout (drop the per-page duplicates),
repoint detail-page back links at their section pages, and remove the now-dead
SectionHeader component / SECTION_HEADERS map (each page owns its header).

app/src/components/ScheduledSection.tsx

@@ -2,7 +2,6 @@ import { Link } from "react-router-dom"
 import { Play, RefreshCw, Square } from "lucide-react"
 import type { JobSummary, HealthStatus } from "@/types"
 import { useServiceAction } from "@/services/api/hooks"
-import { SectionHeader } from "./SectionHeader"
 import { StackBadge } from "./StackBadge"
 
 interface ScheduledSectionProps {
@@ -14,10 +13,8 @@ export function ScheduledSection({ jobs, statuses }: ScheduledSectionProps) {
   const statusMap = new Map(statuses.map((s) => [s.id, s]))
 
   return (
-    <section>
-      <SectionHeader section="scheduled" />
-      <div className="border border-[var(--border)] rounded-lg overflow-x-auto">
-        <table className="w-full min-w-[36rem] text-sm">
+    <div className="border border-[var(--border)] rounded-lg overflow-x-auto">
+      <table className="w-full min-w-[36rem] text-sm">
           <thead>
             <tr className="bg-[var(--card)] border-b border-[var(--border)] text-left">
               <th className="px-3 py-2 font-medium text-[var(--muted)]">Name</th>
@@ -33,8 +30,7 @@ export function ScheduledSection({ jobs, statuses }: ScheduledSectionProps) {
             ))}
           </tbody>
         </table>
-      </div>
-    </section>
+    </div>
   )
 }