feat(cra): scanner-repo→IACE-Projekt-Mapping persistieren (Pull-Flow) [migration-approved]

Ersetzt die ephemere Dropdown-Auswahl durch DB-Persistenz pro IACE-Projekt:
- Migration 156: compliance_cra_scanner_repo_map (tenant_id, iace_project_id PK,
  scanner_repo_id). Additiv + idempotent.
- GET/PUT /v1/cra/scanner-repo-map/{iace_project_id} (Upsert/Clear).
- useCRA lädt das gespeicherte Repo beim Laden + persistiert bei Auswahl.

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

backend-compliance/migrations/156_cra_scanner_repo_map.sql

@@ -0,0 +1,12 @@
+-- Migration 156: persist the scanner repo chosen per IACE project for the
+-- CRA/Cyber pull-flow (replaces the ephemeral UI dropdown selection). Keyed by
+-- IACE project id so it works for any project, independent of a linked CRA
+-- project. Additive + idempotent.
+
+CREATE TABLE IF NOT EXISTS compliance_cra_scanner_repo_map (
+    tenant_id        UUID NOT NULL,
+    iace_project_id  UUID NOT NULL,
+    scanner_repo_id  TEXT NOT NULL,
+    updated_at       TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    PRIMARY KEY (tenant_id, iace_project_id)
+);