fix(mock-data): Fake-Daten bei leerer DB entfernt — ISMS 0%, Dashboard keine simulierten Trends, Compliance-Hub keine Fallback-Zahlen

- ISMS Overview: 14% → 0% bei leerer DB, "not_started" Status, alle Kapitel 0%
- Dashboard: 12-Monate simulierte Trend-Historie entfernt
- Compliance-Hub: Hardcoded Fallback-Statistiken (474/180/95/120/79/44/558/19) → 0
- SQLAlchemy Bug: `is not None` → `.isnot(None)` in SoA-Query
- Hardcoded chapter_7/8_status="pass" → berechnet aus Findings

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend-compliance/tests/test_isms_routes.py

@@ -821,14 +821,18 @@ class TestOverviewDashboard:
     """Tests for the ISO 27001 overview endpoint."""
 
     def test_overview_empty_isms(self):
-        """GET /isms/overview on empty DB should return not_ready."""
+        """GET /isms/overview on empty DB should return not_started with 0% readiness."""
         r = client.get("/isms/overview")
         assert r.status_code == 200
         body = r.json()
-        assert body["overall_status"] in ("not_ready", "at_risk")
+        assert body["overall_status"] == "not_started"
+        assert body["certification_readiness"] == 0.0
         assert body["scope_approved"] is False
         assert body["open_major_findings"] == 0
         assert body["policies_count"] == 0
+        # All chapters should show 0% on empty DB
+        for ch in body["chapters"]:
+            assert ch["completion_percentage"] == 0.0, f"Chapter {ch['chapter']} should be 0% on empty DB"
 
     def test_overview_with_data(self):
         """GET /isms/overview should reflect created data."""