feat(halachot): Phase 5 — canonical panel UI + instances accordion (V41)

UI changes to halacha-review-panel.tsx:
- instance_type badge (עיקרון מקורי / ציטוט / יישום) in meta row
- "מוזכר ב-N פסיקות" pill when instance_count > 1
- CanonicalSection component: canonical_statement (view + edit), instances accordion

Backend:
- list_halachot SQL: adds canonical_id, instance_type, canonical_statement,
  instance_count via LEFT JOIN canonical_halachot
- list_canonical_instances(canonical_id) → compact rows for accordion
- GET /api/canonical-halachot/{canonical_id}/instances endpoint
- PATCH /api/halachot/{id}: canonical_statement propagates to canonical_halachot
- HalachaUpdateRequest: canonical_statement field
- useCanonicalInstances hook + CanonicalInstance type in precedent-library.ts

INV-G10 (chair gate): only the chair can edit canonical_statement (same
flow as rule_statement — PATCH /api/halachot/{id} with reviewer="דפנה").
G2: canonical data flows through canonical_halachot, not a parallel store.

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

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

@@ -126,6 +126,11 @@ export type Halacha = {
       reason: string;
     }[];
   };
+  /* V41 — canonical halachot model: one principle, many instances. */
+  canonical_id?: string | null;
+  instance_type?: "original" | "citation" | "application" | null;
+  canonical_statement?: string | null;
+  instance_count?: number | null;
 };
 
 export type RelatedCase = {
@@ -671,8 +676,31 @@ export type HalachaPatch = Partial<{
   // #133 — editing the quote re-verifies it against the source server-side and
   // clears/sets the quote_unverified flag (extraction repair).
   supporting_quote: string;
+  // V41 — propagated to canonical_halachot.canonical_statement
+  canonical_statement: string;
 }>;
 
+export type CanonicalInstance = {
+  id: string;
+  instance_type: "original" | "citation" | "application";
+  confidence: number;
+  rule_statement: string;
+  case_number: string;
+  case_name: string;
+};
+
+export function useCanonicalInstances(canonical_id: string | null | undefined) {
+  return useQuery({
+    queryKey: ["canonical-instances", canonical_id],
+    queryFn: () =>
+      apiRequest<{ instances: CanonicalInstance[] }>(
+        `/api/canonical-halachot/${encodeURIComponent(canonical_id!)}/instances`,
+      ).then((r) => r.instances),
+    enabled: !!canonical_id,
+    staleTime: 60_000,
+  });
+}
+
 export function useUpdateHalacha() {
   const qc = useQueryClient();
   return useMutation({