feat(ai-sdk): demote superseded pre-eu-v1 sources in authority rerank

The old pre-eu-v1 corpus chunks (un-annotated CRA/AI Act/DORA/NIS2/DSGVO
duplicates + the old Machinery Directive and its guide) are tagged
status=superseded / use_for_primary=false in the vector store. Honor that
in the rerank: a superseded result takes a fixed penalty so the eu-v1 norm
wins default questions, while the old source stays in the pool (demoted,
not hidden) and remains findable for history / transition questions.

Verified on dev: "CRA Sicherheitsupdates" now returns CRA Anhang I (eu-v1)
at #1 instead of an un-annotated old chunk; MaschinenVO outranks the old
Machinery Directive/guide; superseded chunks remain retrievable lower down.

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

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

@@ -0,0 +1,30 @@
+package ucca
+
+import "testing"
+
+// A superseded alt-source must rank below the same result when it is NOT
+// superseded (the eu-v1 norm), but only demoted — the penalty is finite, so it
+// stays in the pool and remains findable for history/transition questions.
+func TestAuthorityScore_SupersededIsDemotedNotRemoved(t *testing.T) {
+	fresh := LegalSearchResult{
+		Score: 0.65, SourceClass: "binding_law", AuthorityWeight: 100,
+		Jurisdiction: "EU", RegulationShort: "CRA", Article: "13",
+	}
+	old := fresh
+	old.Superseded = true
+
+	sFresh := authorityScore("CRA Sicherheitsupdates Hersteller", fresh, "", false)
+	sOld := authorityScore("CRA Sicherheitsupdates Hersteller", old, "", false)
+
+	if sOld >= sFresh {
+		t.Errorf("superseded must score lower: fresh=%.3f superseded=%.3f", sFresh, sOld)
+	}
+	gap := sFresh - sOld
+	if gap < supersededPenalty-0.001 || gap > supersededPenalty+0.001 {
+		t.Errorf("demotion should equal supersededPenalty (%.2f), got %.3f", supersededPenalty, gap)
+	}
+	// Still a positive, finite score → present in the pool, not hidden.
+	if sOld <= -1 {
+		t.Errorf("superseded score collapsed (%.3f) — must remain findable", sOld)
+	}
+}