fix(ai-sdk): national-law subsidiarity in authority rerank (DSGVO > BDSG for general questions)

The authority reranker (wired in legal_rag_client.go:168) had no national-subsidiarity
dimension, so a general BDSG paragraph could outrank the primary DSGVO article. Surfaced by
the KB-2026.1 BDSG pilot (dp_05/08/11 + cr_07).

- authorityScore: DE binding_law in an EU-primary domain WITHOUT a co-primary topic match
  -> soft demote (subsidiarityPen 0.18), not exclusion. National special rules stay
  co-primary via the topic ontology (DSB Art.37+§38, special categories Art.9+§22, ...).
- queryDomain: fall back to a regulation-name mention (DSGVO/BDSG/CRA) so a question phrased
  around the act is domain-scoped even without a topical keyword (fixes cr_07: BDSG Teil-3 §64).
- data_protection keyword stem 'auftragsverarbeit' (catches Auftragsverarbeitungsvertrag).

Pure ranking logic, no data manipulation; soft demotes keep national rules visible.
Build result (DSGVO+BDSG): degraded=0, must_not=0. go build/vet/test ./... green; 6 new table tests.

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

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

@@ -14,6 +14,7 @@ const (
 	domainMatchGain   = 0.15
 	offDomainPenalty  = 0.10 // off-domain binding (demoted, not removed)
 	scopePenalty      = 0.25 // BDSG Teil 3 (law enforcement) on a general DP question
+	subsidiarityPen   = 0.18 // national implementing law (BDSG) on a general EU-primary question: SOFT demote, not exclusion
 	topicGain         = 0.18 // amplifier only
 	supersededPenalty = 0.50 // superseded Alt-Quelle (pre-eu-v1): demoted, nicht versteckt
 	intentLiftGain    = 0.10 // epsilon a qualifying interpretative source is lifted ABOVE the best binding
@@ -102,6 +103,15 @@ func authorityScore(query string, r LegalSearchResult, qDomain string, qForeign
 	if qDomain == "data_protection" && scopeClass(r) == "law_enforcement" {
 		score -= scopePenalty
 	}
+	// Subsidiarity: a national implementing law (DE binding, e.g. BDSG) is subsidiary to the
+	// primary EU act for GENERAL questions in an EU-primary domain — UNLESS the query hits a
+	// topic where the national norm is co-primary (DSB §38, special categories §22, ...). The
+	// topic boost below lifts those; here we only SOFT-demote the non-topic national norm, so
+	// it stays visible and can still win on a strongly matching topic. No hard exclusion.
+	if euPrimaryDomains[qDomain] && info.sourceClass == "binding_law" &&
+		info.jurisdiction == "DE" && !resultMatchesTopic(query, r) {
+		score -= subsidiarityPen
+	}
 	if resultMatchesTopic(query, r) {
 		score += topicGain // Verstaerker, kein Override
 	}