fix(doctor): exclude merge artifacts from multiple JSONL warning

Add .base.jsonl, .left.jsonl, and .right.jsonl patterns to the skip list
in CheckLegacyJSONLFilename. These are legitimate git merge conflict
artifacts that should not trigger a warning about multiple JSONL files.

Fixes: bd-nsb

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

cmd/bd/doctor/legacy.go

@@ -139,7 +139,11 @@ func CheckLegacyJSONLFilename(repoPath string) DoctorCheck {
 			strings.Contains(lowerName, ".bak") ||
 			strings.Contains(lowerName, "~") ||
 			strings.HasPrefix(lowerName, "backup_") ||
-			name == "deletions.jsonl" {
+			name == "deletions.jsonl" ||
+			// Git merge conflict artifacts (e.g., issues.base.jsonl, issues.left.jsonl)
+			strings.Contains(lowerName, ".base.jsonl") ||
+			strings.Contains(lowerName, ".left.jsonl") ||
+			strings.Contains(lowerName, ".right.jsonl") {
 			continue
 		}