feat(ai-sdk): authority-aware re-ranking for legal RAG retrieval (Phase 1)

Re-orders /sdk/v1/rag/search results so binding law from the matching
jurisdiction and domain ranks above guidance, foreign and off-domain law —
without dropping anything (guidance stays as interpretation context).
Internal-only: response schema is unchanged (json:"-" fields), so every
consumer benefits without a contract change.

- authority.go: classifyAuthority / queryDomain / chunkDomain / scopeClass /
  topic ontology. Tagged payload (authority_weight/source_class/jurisdiction)
  wins; deterministic fallback via category + name markers for the untagged corpus.
- authority_rerank.go: rerankByAuthority. final = semantic + authority +
  jurisdiction + domain + scope + topic; the authority score is written back to
  Score so the multi-collection advisor merge preserves the order.
- legal_rag_client: stratified retrieval — the binding-law pool AUGMENTS the
  semantic pool (mergeDedupHits), then re-rank.
- legal_rag_http: searchBinding (source_class filter) + shared doPointsSearch.
- table-driven tests for authority/domain/scope/topic + rerank acceptance +
  a stratified-binding integration test. go test -race green.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ai-compliance-sdk/internal/ucca/legal_rag_scroll.go

@@ -225,6 +225,18 @@ func getIntSlice(m map[string]interface{}, key string) []int {
 	return result
 }
 
+func getInt(m map[string]interface{}, key string) int {
+	if v, ok := m[key]; ok {
+		switch n := v.(type) {
+		case float64:
+			return int(n)
+		case int:
+			return n
+		}
+	}
+	return 0
+}
+
 func contains(slice []string, item string) bool {
 	for _, s := range slice {
 		if s == item {