feat: bootstrap FastAPI configuration

tests/test_config.py

@@ -0,0 +1,32 @@
+from pathlib import Path
+
+from app.config import Settings
+
+
+def test_settings_build_default_data_paths(tmp_path: Path) -> None:
+    settings = Settings(
+        ADMIN_PASSWORD="admin-secret",
+        SECRET_KEY="session-secret-16chars",
+        CREDENTIAL_ENCRYPTION_KEY="ZmFrZS1rZXktZm9yLXRlc3RzLW11c3QtYmUtNDQtY2hhcnM=",
+        DATA_DIR=str(tmp_path),
+        SYNC_INTERVAL_MINUTES=5,
+    )
+
+    assert settings.data_dir == tmp_path
+    assert settings.database_url == f"sqlite:///{tmp_path / 'app.db'}"
+    assert settings.tokens_dir == tmp_path / "tokens"
+    assert settings.activities_dir == tmp_path / "activities"
+
+
+def test_sync_interval_must_be_positive(tmp_path: Path) -> None:
+    try:
+        Settings(
+            ADMIN_PASSWORD="admin-secret",
+            SECRET_KEY="session-secret-16chars",
+            CREDENTIAL_ENCRYPTION_KEY="ZmFrZS1rZXktZm9yLXRlc3RzLW11c3QtYmUtNDQtY2hhcnM=",
+            DATA_DIR=str(tmp_path),
+            SYNC_INTERVAL_MINUTES=0,
+        )
+    except ValueError:
+        return
+    raise AssertionError("Expected validation failure for non-positive interval")