fix: address self-review findings

- Remove dead code: findOwnReview (replaced by findAllOwnReviews)
- Check SetRetryBackoff return value in doJSONRequest tests
- Extract doWithRetry shared helper to eliminate ~100 lines of
  duplicated 429-retry/backoff/Retry-After logic between doRequest
  and doJSONRequest
- Fix import order: context before encoding/json (goimports)
- Add slog.Warn when ListReviews hits maxReviewPages limit

github/reviews.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"log/slog"
 	"net/http"
 	"net/url"
 
@@ -139,6 +140,11 @@ func (c *Client) ListReviews(ctx context.Context, owner, repo string, number int
 		if len(reviews) < reviewsPerPage {
 			break
 		}
+		if page == maxReviewPages {
+			slog.Warn("ListReviews hit page limit; results may be truncated",
+				"owner", owner, "repo", repo, "pr", number,
+				"maxPages", maxReviewPages, "reviewsFetched", len(allReviews))
+		}
 	}
 
 	return allReviews, nil