Refactor test cases for improved readability and consistency

- Updated test functions in various test files to enhance code clarity by formatting long lines and improving indentation.
- Adjusted assertions to use multi-line formatting for better readability.
- Added new test cases for theme settings API to ensure proper functionality.
- Ensured consistent use of line breaks and spacing across test files for uniformity.

tests/e2e/test_consumption.py

@@ -7,7 +7,9 @@ def test_consumption_form_loads(page: Page):
     """Verify the consumption form page loads correctly."""
     page.goto("/ui/consumption")
     expect(page).to_have_title("Consumption · CalMiner")
-    expect(page.locator("h2:has-text('Add Consumption Record')")).to_be_visible()
+    expect(
+        page.locator("h2:has-text('Add Consumption Record')")
+    ).to_be_visible()
 
 
 def test_create_consumption_item(page: Page):