fix: skip interactions.jsonl in FindJSONLInDir (GH#709)

FindJSONLInDir() was returning interactions.jsonl when issues.jsonl
didn't exist. This caused bd sync to write issue data to the wrong
file after fresh init.

Add interactions.jsonl to the skip list alongside deletions.jsonl
and merge artifacts, so the function correctly defaults to issues.jsonl.

internal/utils/path_test.go

@@ -110,6 +110,16 @@ func TestFindJSONLInDir(t *testing.T) {
 			files:    []string{"deletions.jsonl"},
 			expected: "issues.jsonl",
 		},
+		{
+			name:     "only interactions.jsonl - returns default issues.jsonl",
+			files:    []string{"interactions.jsonl"},
+			expected: "issues.jsonl",
+		},
+		{
+			name:     "interactions.jsonl with issues.jsonl - prefers issues",
+			files:    []string{"interactions.jsonl", "issues.jsonl"},
+			expected: "issues.jsonl",
+		},
 		{
 			name:     "only merge artifacts - returns default issues.jsonl",
 			files:    []string{"beads.base.jsonl", "beads.left.jsonl", "beads.right.jsonl"},