Fix format2tidy KeyError by using dynamic column name

The pd.melt(df.T) call produces column names based on the DataFrame's
MultiIndex level names, which may not always be 'Subject'. This fix
dynamically retrieves the actual column name after melt instead of
hardcoding it.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: jeremymanning

quail/helpers.py

@@ -53,9 +53,12 @@ def make_multi_index(listindex, sub_num):
 
 def format2tidy(df, subjname, listname, subjgroup, analysis=None, position=0):
     melted_df = pd.melt(df.T)
+    # Get the actual column name for subjects (first column after melt)
+    # This may be 'Subject' or the actual index level name from the DataFrame
+    subject_col = melted_df.columns[0]
     melted_df[subjname]=""
-    for idx,sub in enumerate(melted_df['Subject'].unique()):
-        melted_df.loc[melted_df['Subject']==sub,subjname]=subjgroup[idx]
+    for idx,sub in enumerate(melted_df[subject_col].unique()):
+        melted_df.loc[melted_df[subject_col]==sub,subjname]=subjgroup[idx]
     if analysis=='spc':
         base = list(df.columns)
         melted_df['Position'] = base * int(melted_df.shape[0] / len(base))