feat(cmp): unified consent view — Website-Besucher + Login-Nutzer tabs

Merges two separate consent views into one unified page at /sdk/einwilligungen:
- Tab "Website-Besucher": device-based banner consents with site selector
- Tab "Login-Nutzer": user-based DSGVO consents (existing, unchanged)

Backend:
- New endpoint GET /admin/consents for paginated banner consent records
- Fix: categories JSON string parsing (was iterating chars instead of array)

CMP Dashboard:
- Dynamic site selector replacing hardcoded "preview-test-site"

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend-compliance/compliance/api/banner_routes.py

@@ -204,6 +204,19 @@ async def get_site_stats(
         return service.get_site_stats(tenant_id, site_id)
 
 
+@router.get("/admin/consents")
+async def list_banner_consents(
+    site_id: str | None = None,
+    limit: int = 50,
+    offset: int = 0,
+    tenant_id: str = Depends(_get_tenant),
+    service: BannerConsentService = Depends(get_consent_service),
+) -> dict[str, Any]:
+    """Paginated list of banner consents for admin dashboard."""
+    with translate_domain_errors():
+        return service.list_consents(tenant_id, site_id, limit, offset)
+
+
 # =============================================================================
 # Admin — Sites
 # =============================================================================