feat: configure minimum splash duration

tests/test_config.py

@@ -10,6 +10,7 @@ def test_paths_and_automation_settings_round_trip(tmp_path, monkeypatch) -> None
         gnucash_path=str(tmp_path / "club.gnucash"),
         theme_mode="light",
         run_housekeeper_on_startup=False,
+        splash_minimum_seconds=0,
         birthday_days_before=10,
         birthday_days_after=3,
         anniversary_days_before=21,
@@ -26,6 +27,16 @@ def test_paths_and_automation_settings_round_trip(tmp_path, monkeypatch) -> None
     raw = json.loads(expected.path.read_text(encoding="utf-8"))
     assert raw["schema_version"] == 1
     assert raw["monitor_bounds"] == [-1920, 0, 1920, 1080]
+    assert raw["splash_minimum_seconds"] == 0
+
+
+def test_splash_minimum_defaults_to_five_and_is_clamped(tmp_path, monkeypatch) -> None:
+    monkeypatch.setenv("CCMA_CONFIG_DIR", str(tmp_path / "config"))
+    assert load_config().splash_minimum_seconds == 5.0
+
+    config = AppConfig(splash_minimum_seconds=-10)
+    config.save()
+    assert load_config().splash_minimum_seconds == 0.0
 
 
 def test_legacy_c3ma_environment_variables_are_still_read(tmp_path, monkeypatch) -> None: