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_eval_warnings_extended.py

@@ -0,0 +1,77 @@
+"""Extended tests for python/eval_warnings/main.py."""
+
+from __future__ import annotations
+
+import os
+from pathlib import Path
+from unittest.mock import MagicMock, patch
+
+from python.eval_warnings.main import (
+    EvalWarning,
+    extract_referenced_files,
+)
+
+
+def test_extract_referenced_files_nix_store_paths(tmp_path: Path) -> None:
+    """Test extracting files from nix store paths."""
+    # Create matching directory structure
+    systems_dir = tmp_path / "systems"
+    systems_dir.mkdir()
+    nix_file = systems_dir / "test.nix"
+    nix_file.write_text("{ pkgs }: pkgs")
+
+    warnings = {
+        EvalWarning(
+            system="s1",
+            message="warning: in /nix/store/abc-source/systems/test.nix:5: deprecated",
+        )
+    }
+
+    # Change to tmp_path so relative paths work
+    old_cwd = os.getcwd()
+    try:
+        os.chdir(tmp_path)
+        files = extract_referenced_files(warnings)
+    finally:
+        os.chdir(old_cwd)
+
+    assert "systems/test.nix" in files
+    assert files["systems/test.nix"] == "{ pkgs }: pkgs"
+
+
+def test_extract_referenced_files_no_files_found() -> None:
+    """Test extract_referenced_files when no files are found."""
+    warnings = {
+        EvalWarning(
+            system="s1",
+            message="warning: something generic without file paths",
+        )
+    }
+    files = extract_referenced_files(warnings)
+    # Either empty or has flake.nix fallback
+    assert isinstance(files, dict)
+
+
+def test_extract_referenced_files_repo_relative_paths(tmp_path: Path) -> None:
+    """Test extracting repo-relative file paths."""
+    # Create the referenced file
+    systems_dir = tmp_path / "systems" / "foo"
+    systems_dir.mkdir(parents=True)
+    nix_file = systems_dir / "bar.nix"
+    nix_file.write_text("{ config }: {}")
+
+    warnings = {
+        EvalWarning(
+            system="s1",
+            message="warning: in systems/foo/bar.nix:10: test",
+        )
+    }
+
+    old_cwd = os.getcwd()
+    try:
+        os.chdir(tmp_path)
+        files = extract_referenced_files(warnings)
+    finally:
+        os.chdir(old_cwd)
+
+    assert "systems/foo/bar.nix" in files