fix: 遗留清理（枚举同源/边界防御/断言补强）

tests/test_formatting_detector.py

@@ -35,6 +35,19 @@ def test_cell_formatting_none_when_plain():
     assert cell_formatting(ws["A1"]) is None
 
 
+def test_cell_formatting_detects_font_color():
+    from openpyxl.styles import Font
+    wb = Workbook()
+    ws = wb.active
+    ws["A1"] = "x"
+    f = copy(ws["A1"].font)
+    f.color = Font(color="FF0000FF").color
+    ws["A1"].font = f
+    fmt = cell_formatting(ws["A1"])
+    assert fmt is not None
+    assert fmt.font_color is not None
+
+
 def test_cell_comment_returns_obj():
     wb = make_wb()
     cm = cell_comment(wb.active["A2"], "f.xlsx")