feat(web): FE overhaul — SWR centralized data layer + dashboard + islands

- Add SWR foundation (lib/fetcher, lib/swr, lib/api) with typed
  hooks: useSections/useDocuments/useSearch/useRelated/useRevisions/useQueueStatus
- Replace ad-hoc useEffect+fetch in Header/Sidebar/CommandMenu/search
  with SWR (dedup 4s, focus throttle 10s, debounced search 180ms)
- Doc page: RelatedGrid + RevisionList as SWR client islands (RSC hero stays)
- DocForm: SWR mutate on create/update for live sidebar invalidation
- New APIs: /api/related, /api/revisions, /api/tags, /api/queue/status,
  /api/docs filtering (?section=&status=)
- New UI: DocumentCard, SectionCard, SearchBar, TagCloud, QueueBadge,
  EmptyState, dashboard (/dashboard with QueueStrip live + section stats)
- Layout wraps SWRProvider; no TanStack code (SWR-only per spec)
- Verified: next build passes (16.3.4 Turbopack), no manual fetch sprawl remains

Co-Authored-By: internal-model

apps/web/app/lib/swr.tsx

@@ -0,0 +1,19 @@
+"use client";
+
+import { SWRConfig } from "swr";
+
+export default function SWRProvider({ children }: { children: React.ReactNode }) {
+  return (
+    <SWRConfig
+      value={{
+        dedupingInterval: 4_000,
+        focusThrottleInterval: 10_000,
+        revalidateOnFocus: true,
+        shouldRetryOnError: false,
+        errorRetryCount: 0,
+      }}
+    >
+      {children}
+    </SWRConfig>
+  );
+}