fix: prevent self-merge in consolidateDuplicates (issue #25)

[tryweb]

Summary

• Fix bug where consolidateDuplicates could produce self-referencing records
• When two records have identical timestamps, they could be treated as merge candidates with themselves
• Added ID check before merge to skip self-merge cases

Changes

const older = a.row.timestamp <= b.row.timestamp ? a.row : b.row;
const newer = a.row.timestamp <= b.row.timestamp ? b.row : a.row;

+// Skip self-merge: when timestamps are equal, both could reference the same record
+if (older.id === newer.id) {
+  continue;
+}

Fixes #25