fix(data-platform): reset index after filter to prevent extra column

The filter tool was adding an __index_level_0__ column to results
because pandas query() preserves the original index, which gets
converted to a column when storing the DataFrame.

Added .reset_index(drop=True) after query() to drop the preserved
index and create a clean sequential index.

Fixes #203

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

mcp-servers/data-platform/mcp_server/pandas_tools.py

@@ -330,7 +330,7 @@ class PandasTools:
             return {'error': f'DataFrame not found: {data_ref}'}
 
         try:
-            filtered = df.query(condition)
+            filtered = df.query(condition).reset_index(drop=True)
             result_name = name or f"{data_ref}_filtered"
             return self._check_and_store(
                 filtered,