Add comprehensive test suite achieving 99% code coverage

Added 35 test files with 502 tests covering all Python modules including
API routes, ORM models, splendor game logic/TUI, heater controller,
weather service, NixOS installer, ZFS dataset management, and utilities.
Coverage improved from 11% to 99% (2540/2564 statements covered).

https://claude.ai/code/session_01SVzgLDUS1Cdc4eh1ijETTh

tests/test_heater_main.py

@@ -0,0 +1,43 @@
+"""Tests for python/heater/main.py."""
+
+from __future__ import annotations
+
+import sys
+from unittest.mock import MagicMock, patch
+
+from python.heater.models import ActionResult, DeviceConfig, HeaterStatus
+
+
+def test_create_app() -> None:
+    """Test create_app creates FastAPI app."""
+    mock_tinytuya = MagicMock()
+    with patch.dict(sys.modules, {"tinytuya": mock_tinytuya}):
+        if "python.heater.controller" in sys.modules:
+            del sys.modules["python.heater.controller"]
+        if "python.heater.main" in sys.modules:
+            del sys.modules["python.heater.main"]
+        from python.heater.main import create_app
+
+        config = DeviceConfig(device_id="abc", ip="10.0.0.1", local_key="key")
+        app = create_app(config)
+        assert app is not None
+        assert app.title == "Heater Control API"
+
+
+def test_serve_missing_params() -> None:
+    """Test serve raises with missing parameters."""
+    import typer
+
+    mock_tinytuya = MagicMock()
+    with patch.dict(sys.modules, {"tinytuya": mock_tinytuya}):
+        if "python.heater.controller" in sys.modules:
+            del sys.modules["python.heater.controller"]
+        if "python.heater.main" in sys.modules:
+            del sys.modules["python.heater.main"]
+        from python.heater.main import serve
+
+        with patch("python.heater.main.configure_logger"):
+            try:
+                serve(host="0.0.0.0", port=8124, log_level="INFO")
+            except (typer.Exit, SystemExit):
+                pass