Add trim CLI command

internal/trim/apply.go

@@ -95,6 +95,9 @@ func Apply(input schema.Transcript, opts Options) (Result, error) {
 	}
 
 	kept, groups := recomputeOverlapGroups(kept)
+	if groups == nil {
+		groups = make([]schema.OverlapGroup, 0)
+	}
 
 	out := copyTranscript(input)
 	out.Segments = kept
@@ -278,7 +281,7 @@ func validateSelectedIDsExist(selected []int, idIndex map[int]int) error {
 
 func recomputeOverlapGroups(segments []schema.Segment) ([]schema.Segment, []schema.OverlapGroup) {
 	if len(segments) == 0 {
-		return segments, nil
+		return segments, make([]schema.OverlapGroup, 0)
 	}
 
 	modelSegments := make([]model.Segment, len(segments))