fix: guard mzenumeration column check in _merge_filter_cardinality for MS1 data

[abhi-0203]

Summary

CARDINALITY qualifier on an MS1 condition raises KeyError: 'mzenumeration' because MS1 peak data lacks the mzenumeration column that the MS2 processing pipeline adds.

Root cause: _merge_filter_cardinality does groupby(["scan", "mzenumeration"]) on the concatenated peak DataFrame. MS2 data has mzenumeration (set at line 271 before appending to ms2_list), but MS1 data never gets this column assigned, so the groupby raises KeyError.

Fix: Add a column-existence guard before the groupby — if mzenumeration is absent, return the peak DataFrame unchanged. This is the correct behavior since cardinality filtering is an MS2-specific concept and should be a no-op for MS1 scans.

Changes

massql/msql_engine_filters.py

Added 4 lines to _merge_filter_cardinality:

if "mzenumeration" not in ms_peak_df.columns:
    # MS1 data does not have per-peak enumeration — cardinality filtering is not applicable
    return ms_peak_df

Closes #264