feat(graph): navigation & UX — deep-link, depth, PNG, rich panel (PR D)

Final corpus-graph PR. Connects the graph to the chair's workflow and rounds
out the Obsidian-grade interactions.

Backend (web/graph_api.py): neighborhood depth cap 2 → 3 (still bounded by
NODE_CAP_MAX).

Frontend:
- URL deep-link: /graph?focus=cl:<id> is read on mount and written on focus
  change (router.replace, scroll:false). GraphView wrapped in <Suspense> per
  Next 16's useSearchParams requirement.
- "הצג בגרף" button on the precedent detail page → /graph?focus=cl:<id>.
- Depth slider (1–3) in the focused overlay → useNodeNeighborhood(id, depth).
- Export PNG: grabs the rendered <canvas> from the area ref → toDataURL →
  download; failures surface a toast (UI4).
- Rich node panel: precedent nodes fetch headnote/summary via the existing
  usePrecedent hook (Skeleton while pending, error surfaced — UI4).
- Edge-type legend (ציטוט / נושא-תחום / יומון) added under the node legend.

Deferred (noted for a later pass): expand-in-place merge, search→camera-center.

web-ui build + lint pass. Invariants: G2 (depth change is read-only), UI4
(PNG + detail errors surfaced, not swallowed). api:types post-deploy.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web-ui/src/app/graph/page.tsx

@@ -1,3 +1,4 @@
+import { Suspense } from "react";
 import Link from "next/link";
 
 import { AppShell } from "@/components/app-shell";
@@ -22,7 +23,15 @@ export default function GraphPage() {
           </p>
         </header>
         <div className="h-[2px] bg-gradient-to-l from-transparent via-gold to-transparent" />
-        <GraphView />
+        <Suspense
+          fallback={
+            <div className="grid h-[560px] place-items-center text-sm text-ink-muted">
+              טוען גרף…
+            </div>
+          }
+        >
+          <GraphView />
+        </Suspense>
       </section>
     </AppShell>
   );