fix: guard non-string writing_preset against TypeError on load

Eine manuell editierte config.json mit einem unhashbaren Wert (Liste/Objekt)
für workflows.writing_preset löste in _validate_and_sanitize einen TypeError
aus (`value not in set` hasht den Wert) und brach den Start ab, statt auf
"standard" zurückzufallen. Jetzt wird zuerst der String-Typ geprüft.

Adressiert Codex-PR-Review (P2) auf PR #5.

Author: TimInTech

app/config.py

@@ -337,7 +337,8 @@ def _validate_and_sanitize(self) -> None:
             wf["text_improver_tone"] = "neutral"
         if wf.get("emoji_density") not in VALID_EMOJI_DENSITIES:
             wf["emoji_density"] = "mittel"
-        if wf.get("writing_preset") not in VALID_WRITING_PRESETS:
+        preset_value = wf.get("writing_preset")
+        if not isinstance(preset_value, str) or preset_value not in VALID_WRITING_PRESETS:
             wf["writing_preset"] = DEFAULT_PRESET_KEY
         wf["custom_terms"] = _sanitize_terms(wf.get("custom_terms"))
 

tests/test_config.py

@@ -120,6 +120,19 @@ def test_missing_preset_key_defaults_to_standard(self, config_dir):
         assert loaded.writing_preset == "standard"
         assert loaded.text_improver_tone == "formal"
 
+    @pytest.mark.parametrize("bad_value", [[], {}, ["email_formal"], 42, None, True])
+    def test_non_string_preset_value_is_coerced_without_crash(self, config_dir, bad_value):
+        # Manuell editierte config.json mit unhashbarem/falschem Typ darf den
+        # Start nicht mit TypeError abbrechen, sondern auf "standard" zurückfallen.
+        config_dir.mkdir(parents=True, exist_ok=True)
+        (config_dir / "config.json").write_text(
+            json.dumps({"workflows": {"writing_preset": bad_value}}),
+            encoding="utf-8",
+        )
+
+        loaded = BlitztextConfig(config_dir=config_dir)
+        assert loaded.writing_preset == "standard"
+
 
 class TestTranscriptionHotkey:
     def test_valid_hotkey_is_accepted(self, config):