test: add AppSettings defaults and env-parsing smoke tests

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_settings.py

@@ -0,0 +1,16 @@
+from smileyface.settings import AppSettings
+
+
+def test_defaults():
+    settings = AppSettings(_env_file=None)
+    assert settings.sqlite_filename == "smiles.db"
+    assert settings.skip_validate is False
+    assert settings.project_dir == ""
+
+
+def test_env_overrides(monkeypatch):
+    monkeypatch.setenv("SMILEYFACE_PROJECT_DIR", "/srv/ut4")
+    monkeypatch.setenv("SMILEYFACE_SKIP_VALIDATE", "true")
+    settings = AppSettings(_env_file=None)
+    assert settings.project_dir == "/srv/ut4"
+    assert settings.skip_validate is True