fix: use 'unknown' for null framework, run gofmt

internal/store/postgres/stats.go

@@ -59,7 +59,7 @@ func (d *DB) GetSummary(ctx context.Context) (*Summary, error) {
 	// Per-framework aggregates for today
 	fwQ := `
 		SELECT
-			COALESCE(source_framework, ''),
+			COALESCE(source_framework, 'unknown'),
 			COUNT(*) FILTER (WHERE type = 'run.start')        AS runs,
 			COUNT(*) FILTER (WHERE type = 'span.end'
 			                   AND payload->'attributes'->>'span_kind' = 'tool') AS tools,