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_client.go

@@ -93,6 +93,13 @@ func (c *LegalRAGClient) searchInternal(ctx context.Context, collection string,
 		hits = denseHits
 	}
 
+	// Stratified: den binding_law-Pool ERGAENZEN (nicht ersetzen), damit die Pflichtquelle
+	// immer Kandidat ist — Guidance bleibt als Auslegungskontext erhalten. Best-effort:
+	// Fehler beim Binding-Query degradieren still auf den semantischen Pool.
+	if bindingHits, bErr := c.searchBinding(ctx, collection, embedding, topK); bErr == nil {
+		hits = mergeDedupHits(hits, bindingHits)
+	}
+
 	results := make([]LegalSearchResult, len(hits))
 	for i, hit := range hits {
 		// Legal-Metadaten nach rag_reingest_spec.md §2: bevorzugt die normalisierten Felder
@@ -121,12 +128,41 @@ func (c *LegalRAGClient) searchInternal(ctx context.Context, collection string,
 			Pages:           getIntSlice(hit.Payload, "pages"),
 			SourceURL:       getString(hit.Payload, "source"),
 			Score:           hit.Score,
+			AuthorityWeight: getInt(hit.Payload, "authority_weight"),
+			SourceClass:     getString(hit.Payload, "source_class"),
+			Jurisdiction:    getString(hit.Payload, "jurisdiction"),
 		}
 	}
 
+	// Authority-aware Re-Ranking: bindendes Recht der passenden Jurisdiktion/Domaene nach
+	// oben, Guidance/Fremdrecht/Off-Domain runter (nichts wird geloescht). Reihenfolge only,
+	// Response-Schema unveraendert. Score traegt den Authority-Score, damit nachgelagerte
+	// Multi-Collection-Merges (Advisor) die Ordnung bewahren.
+	results = rerankByAuthority(query, results)
+	if topK > 0 && len(results) > topK {
+		results = results[:topK]
+	}
+
 	return results, nil
 }
 
+// mergeDedupHits concatenates two hit lists, keeping the first occurrence of each point ID.
+func mergeDedupHits(primary, extra []qdrantSearchHit) []qdrantSearchHit {
+	seen := make(map[string]bool, len(primary)+len(extra))
+	out := make([]qdrantSearchHit, 0, len(primary)+len(extra))
+	for _, list := range [][]qdrantSearchHit{primary, extra} {
+		for _, h := range list {
+			id := fmt.Sprint(h.ID)
+			if seen[id] {
+				continue
+			}
+			seen[id] = true
+			out = append(out, h)
+		}
+	}
+	return out
+}
+
 // FormatLegalContextForPrompt formats the legal context for inclusion in an LLM prompt.
 func (c *LegalRAGClient) FormatLegalContextForPrompt(lc *LegalContext) string {
 	if lc == nil || len(lc.Results) == 0 {