feat: link related precedents across court instances (SCHEMA_V11)

Add ability to mark case_law records as related (e.g. same appeal
through ועדת ערר → מנהלי → עליון):
- DB: case_law_relations join table (bidirectional, V11 migration)
- DB CRUD: add/remove/get_case_law_relations
- Service: get_precedent() now returns related_cases[]
- MCP: precedent_link_cases + precedent_unlink_cases tools
- REST: POST/DELETE /api/precedent-library/{id}/relations
- UI: RelatedCasesSection on detail page with search dialog and unlink

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web-ui/src/lib/api/precedent-library.ts

@@ -84,9 +84,20 @@ export type Halacha = {
   precedent_level?: string;
 };
 
+export type RelatedCase = {
+  id: string;
+  case_number: string;
+  case_name: string;
+  court: string;
+  precedent_level: string;
+  date: string | null;
+  relation_type: string;
+};
+
 export type PrecedentDetail = Precedent & {
   full_text: string;
   halachot: Halacha[];
+  related_cases: RelatedCase[];
 };
 
 export type SearchHit =
@@ -357,6 +368,40 @@ export function useDeletePrecedent() {
   });
 }
 
+export function useLinkRelatedCase(caseId: string) {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (vars: { relatedId: string; relationType?: string }) =>
+      apiRequest<{ linked: boolean }>(
+        `/api/precedent-library/${encodeURIComponent(caseId)}/relations`,
+        {
+          method: "POST",
+          body: {
+            related_id: vars.relatedId,
+            relation_type: vars.relationType ?? "same_case_chain",
+          },
+        },
+      ),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: libraryKeys.detail(caseId) });
+    },
+  });
+}
+
+export function useUnlinkRelatedCase(caseId: string) {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (relatedId: string) =>
+      apiRequest<{ unlinked: boolean }>(
+        `/api/precedent-library/${encodeURIComponent(caseId)}/relations/${encodeURIComponent(relatedId)}`,
+        { method: "DELETE" },
+      ),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: libraryKeys.detail(caseId) });
+    },
+  });
+}
+
 export type PrecedentPatch = Partial<{
   case_name: string;
   court: string;