Phase 12: Test-Suite (30 pytest-Tests) + CLAUDE.md aktualisiert

tests/:
  conftest.py        - minimale Env-Vars + sys.path-Setup
  test_auth.py       - Magic-Token + JWT Round-Trip (4 Tests)
  test_audit.py      - diff() + _to_json() Helper (8 Tests)
  test_models.py     - Pydantic-Validierung (7 Tests)
  test_source_meta.py - Single Source of Truth Konsistenz (7 Tests)
  test_imports.py    - alle Backend-Module importierbar (4 Tests)

requirements-dev.txt: pytest, ftfy, pyflakes

Tests sind reine Unit-Tests (kein DB-Zugriff, kein HTTP-Server),
laufen in <0.5s, geben sofortiges Catch-Net fuer Syntax/Import-Bugs.

Aufruf: PYTHONPATH=src ./venv/bin/python -m pytest tests/ -v

CLAUDE.md erweitert um:
- Sektion Tests (Framework, Pfad, Ausfuehrung)
- Sektion Phasen-Historie (alle 12 Phasen der Aufraeum-Aktion 2026-05-09
  mit kurzer Erklaerung)

tests/test_audit.py

@@ -0,0 +1,51 @@
+"""Tests fuer src/audit.py - diff() + _to_json() Helpers."""
+import json
+from audit import diff, _to_json
+
+
+def test_diff_returns_only_changed_fields():
+    before = {"name": "Alt", "status": "active", "max_users": 5}
+    after  = {"name": "Neu", "status": "active", "max_users": 5}
+    result = diff(before, after)
+    assert result == {"name": {"old": "Alt", "new": "Neu"}}
+
+
+def test_diff_no_changes_returns_none():
+    same = {"a": 1, "b": "x"}
+    assert diff(same, dict(same)) is None
+
+
+def test_diff_with_none_returns_none():
+    assert diff(None, {"a": 1}) is None
+    assert diff({"a": 1}, None) is None
+
+
+def test_diff_added_or_removed_fields():
+    before = {"a": 1}
+    after = {"a": 1, "b": 2}
+    result = diff(before, after)
+    assert result == {"b": {"old": None, "new": 2}}
+
+
+def test_to_json_handles_none():
+    assert _to_json(None) is None
+
+
+def test_to_json_handles_dict():
+    out = _to_json({"x": 1, "y": "hallo"})
+    assert json.loads(out) == {"x": 1, "y": "hallo"}
+
+
+def test_to_json_handles_non_serializable_via_str_default():
+    """Custom Objekte werden via default=str zu Strings."""
+    class Foo:
+        def __str__(self):
+            return "FooObj"
+    out = _to_json({"obj": Foo()})
+    assert "FooObj" in out
+
+
+def test_to_json_preserves_umlauts():
+    """ensure_ascii=False soll deutsche Umlaute durchlassen."""
+    out = _to_json({"name": "Müller"})
+    assert "Müller" in out