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/components/DocForm.tsx

@@ -2,6 +2,7 @@
 
 import { useState, useRef } from "react";
 import { useRouter } from "next/navigation";
+import { mutate } from "swr";
 import Markdown from "./Markdown";
 import {
   Bold,
@@ -210,7 +211,12 @@ export default function DocForm({
       }
 
       const result = await res.json();
+      // Invalidate SWR caches so Sidebar/Header/search reflect the change immediately
+      mutate("/api/docs");
+      mutate("/api/sections");
+      mutate((key) => typeof key === "string" && key.startsWith("/api/tags"));
       router.push(result.doc?.slug ? `/${result.doc.slug}` : "/");
+      router.refresh();
     } catch (err) {
       setError(err instanceof Error ? err.message : String(err));
     } finally {