fix: address Copilot review feedback on PR #416

- Use consistent terminology in confirmation message ("background color"
  to match "text color")
- Tighten test assertions for invalid parameter validation to check
  parameter name and all allowed values instead of loose substring matches
- Remove unrelated calendar_tools.py changes (lambda reformatting, guest
  permissions, query_freebusy) that belong in separate PRs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/gsheets/test_format_sheet_range.py

@@ -338,8 +338,11 @@ async def test_format_invalid_wrap_strategy():
             wrap_strategy="INVALID",
         )
 
-    error_msg = str(exc_info.value).lower()
-    assert "wrap_strategy" in error_msg or "wrap" in error_msg
+    error_msg = str(exc_info.value)
+    assert "wrap_strategy" in error_msg
+    assert "CLIP" in error_msg
+    assert "OVERFLOW_CELL" in error_msg
+    assert "WRAP" in error_msg
 
 
 @pytest.mark.asyncio
@@ -357,8 +360,11 @@ async def test_format_invalid_horizontal_alignment():
             horizontal_alignment="INVALID",
         )
 
-    error_msg = str(exc_info.value).lower()
-    assert "horizontal" in error_msg or "left" in error_msg
+    error_msg = str(exc_info.value)
+    assert "horizontal_alignment" in error_msg
+    assert "CENTER" in error_msg
+    assert "LEFT" in error_msg
+    assert "RIGHT" in error_msg
 
 
 @pytest.mark.asyncio
@@ -376,8 +382,11 @@ async def test_format_invalid_vertical_alignment():
             vertical_alignment="INVALID",
         )
 
-    error_msg = str(exc_info.value).lower()
-    assert "vertical" in error_msg or "top" in error_msg
+    error_msg = str(exc_info.value)
+    assert "vertical_alignment" in error_msg
+    assert "BOTTOM" in error_msg
+    assert "MIDDLE" in error_msg
+    assert "TOP" in error_msg
 
 
 @pytest.mark.asyncio