feat(advisor): evidence-framed header + bindingness contract seam

Rework the Compliance Advisor header ("Diese Antwort stuetzt sich auf")
to describe the EVIDENCE rather than the documents: binding
Rechtsgrundlagen split from Leitlinien (soft-law guidance), a
per-regulation breakdown, plus Abbildungen, Fussnoten and Evidence Units.
No fabricated trust score — objective counts only.

- bindingness is a canonical Legal-KG fact (APEX rule): added an optional
  EvidenceUnit.bindingness contract seam; the FE renders the split from it
  and degrades to a neutral per-regulation breakdown when it is absent
  (SDK/RAG asked via board to populate it in /retrieve).
- evidence-grouping.ts: pure, tested grouping/counting model.
- route.ts: optional `audience` field (tonality) kept out of the retrieval
  question; answers lead with a "Kurz gesagt" summary, structured by theme.
- E2E + unit tests updated for the evidence framing.

Not deployed.

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

admin-compliance/lib/sdk/advisor/contract.ts

@@ -25,6 +25,10 @@ export interface EvidenceUnit {
   url?: string
   regulation_code?: string // preferred key for family grouping (from /retrieve)
   context?: string // knowledge space / domain
+  // Canonical Legal-KG fact (APEX rule): binding norm vs. soft-law guidance. Owned by the
+  // Legal-KG/RAG, not derived in the FE. Absent until /retrieve populates it (board request 2026-07-01);
+  // the FE degrades to a neutral per-regulation breakdown when it is missing.
+  bindingness?: 'binding' | 'guidance'
 }
 
 /** Numbered [n] <-> evidence coupling, produced by the SDK (not parsed from the answer). */