Literature review matrix builder

The two diagnostics are the point: theme coverage counts how many sources carry each tag in a column whose name contains Theme, and a tag with a single source is flagged tentative rather than treated as a finding; column completeness counts non-empty notes per column and flags the ones under half filled. Parsing keeps going past bad lines, so one malformed entry rides along as a title-only row with a warning instead of eating the paste. Everything runs in this tab and nothing persists: leave the page and the matrix is gone, so copy the CSV or print before you close it. No reference manager features live here: no DOI lookup, no style formatting, no duplicate-key merging beyond the flag.