fix(cmd,github): address review feedback on PR #106

- Replace panic() with fmt.Fprintf+os.Exit(1) in provider switch default
  (repo convention: never panic)
- Remove spurious 'event' field from DismissReview payload (GitHub dismiss
  endpoint only documents 'message')
- Change translateReviewEvent default to return 'COMMENT' as canonical
  fallback instead of passing unknown events through to GitHub API
- Refactor supersedeOldReviews to use explicit switch/case with default
  error for exhaustiveness

cmd/review-bot/main.go

@@ -170,7 +170,8 @@ func main() {
 		}
 		client = github.NewClient(*reviewerToken, ghBaseURL)
 	default:
-		panic("unreachable: unhandled provider " + *provider)
+		fmt.Fprintf(os.Stderr, "Error: unhandled provider %q\n", *provider)
+		os.Exit(1)
 	}
 	slog.Info("VCS client initialized", "provider", *provider)
 
@@ -523,7 +524,8 @@ func verdictToEvent(verdict string) vcs.ReviewEvent {
 // For GitHub: dismisses old reviews.
 // For Gitea: edits the review body and resolves inline comments.
 func supersedeOldReviews(ctx context.Context, client vcs.Client, provider, vcsURL, owner, repoName string, prNumber int, oldReviews []vcs.Review, newReviewID int64, sentinel string) error {
-	if provider == "github" {
+	switch provider {
+	case "github":
 		for _, old := range oldReviews {
 			if err := client.DismissReview(ctx, owner, repoName, prNumber, old.ID, "Superseded by new review"); err != nil {
 				slog.Warn("failed to dismiss review", "id", old.ID, "error", err)
@@ -532,9 +534,12 @@ func supersedeOldReviews(ctx context.Context, client vcs.Client, provider, vcsUR
 			}
 		}
 		return nil
+	case "gitea":
+		// Gitea: EditComment + ResolveComment flow
+	default:
+		return fmt.Errorf("supersedeOldReviews: unsupported provider %q", provider)
 	}
 
-	// Gitea: existing EditComment + ResolveComment flow
 	giteaAdapter, ok := client.(*gitea.Adapter)
 	if !ok {
 		return fmt.Errorf("expected gitea.Adapter for gitea provider, got %T", client)