feat(backend): On-demand Browser-Verhaltens-Matrix + Snapshot-Persistenz (Phase 2)

- check_snapshot: update_browser_matrix/load_browser_matrix — migrationsfrei
  in banner_result.browser_matrix (JSONB jsonb_set, eigener scanned_at)
- snapshot_check_routes: POST /snapshots/{id}/browser-behavior/run laeuft
  /scan-matrix LIVE (Re-Crawl je Engine, nur live messbar), persistiert das
  Ergebnis; GET /snapshots/{id}/browser-behavior liefert die gespeicherte
  Matrix ohne Re-Crawl. Profil-Set = 4 Default-Engines + Brave/Chrome/Edge.
- consent-tester multi_browser_scanner: Semaphore(2) gegen OOM (7 Browser
  parallel sprengten das 2g-mem_limit)
- Pydantic-Modell mit Optional[List[...]] (nicht `| None`) → Py3.9-sicher
- Tests: _snapshot_scan_url + Request-Defaults (5)

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

backend-compliance/tests/test_snapshot_browser_behavior.py

@@ -0,0 +1,42 @@
+"""Browser-Verhaltens-Endpoint: URL-Ableitung + Request-Defaults (Phase 2).
+
+Reine Logik ohne DB/HTTP — die Live-Matrix + Persistenz werden im macmini-E2E
+verifiziert. Sichert v.a.: scanbare Homepage-URL korrekt aus dem Snapshot
+abgeleitet und das Request-Modell ist auf Python 3.9 baubar (Optional statt
+`| None` — siehe Pydantic-v2-Falle mit `from __future__ import annotations`)."""
+
+from compliance.api.snapshot_check_routes import (
+    _snapshot_scan_url,
+    BrowserBehaviorRunRequest,
+)
+
+
+def test_url_from_doc_entry_origin():
+    snap = {"site_domain": "bmw.de",
+            "doc_entries": [{"url": "https://www.bmw.de/de/impressum.html"}]}
+    assert _snapshot_scan_url(snap) == "https://www.bmw.de"
+
+
+def test_url_falls_back_to_site_domain():
+    assert _snapshot_scan_url({"site_domain": "example.com",
+                               "doc_entries": []}) == "https://example.com"
+
+
+def test_url_skips_blank_entries_then_uses_domain():
+    snap = {"site_domain": "shop.de", "doc_entries": [{"url": ""}, {"url": "  "}]}
+    assert _snapshot_scan_url(snap) == "https://shop.de"
+
+
+def test_url_empty_when_unknown_and_no_entries():
+    assert _snapshot_scan_url({"site_domain": "unknown", "doc_entries": []}) == ""
+    assert _snapshot_scan_url({"site_domain": "", "doc_entries": []}) == ""
+
+
+def test_request_model_defaults_build_on_py39():
+    m = BrowserBehaviorRunRequest()
+    assert m.browser_profiles is None
+    assert m.timeout_per_phase == 10
+    m2 = BrowserBehaviorRunRequest(browser_profiles=["brave-default-de"],
+                                   timeout_per_phase=20)
+    assert m2.browser_profiles == ["brave-default-de"]
+    assert m2.timeout_per_phase == 20