[summary] Filter out large column sets by default

Columns named `C*` and `S*` should be opt-in by default, as they are usually too large.

Start by locating the summary-column filtering entry point in the repository and inspect how default column selection is handled. Verify that columns matching C* and S* are excluded by default while an explicit opt-in still includes them; no file or test is named in the issue.

Written by the indexing model from the issue text.