fix: address review feedback - eliminate type assertion via ReviewSuperseder interface

- Introduce vcs.VCSProvider typed constant (replaces plain string provider)
- Introduce vcs.ReviewSuperseder optional interface for supersede logic
- Implement SupersedeReviews on gitea.Adapter (edit + resolve) and
  github.Client (dismiss)
- Remove concrete type assertion client.(*gitea.Adapter) from main
- Remove redundant baseURL fallback for github (NewClient defaults it)
- Condense --gitea-url alias comment block
- Fix fetchPatterns comment (empty paths are skipped, not fetched)
- Add default panic to VCS client init switch

Addresses: #19607, #19608, #19609, #19610, #19621, #19622, #19623

github/review.go

@@ -210,3 +210,16 @@ func (c *Client) DismissReview(ctx context.Context, owner, repo string, number i
 	}
 	return nil
 }
+
+// SupersedeReviews marks prior reviews as superseded by dismissing them.
+// This implements vcs.ReviewSuperseder for the GitHub adapter.
+// The baseURL and sentinel parameters are unused for GitHub (dismissal is the mechanism).
+func (c *Client) SupersedeReviews(ctx context.Context, owner, repo string, prNumber int, oldReviews []vcs.Review, newReviewID int64, _, _ string) error {
+	var errs []error
+	for _, old := range oldReviews {
+		if err := c.DismissReview(ctx, owner, repo, prNumber, old.ID, "Superseded by new review"); err != nil {
+			errs = append(errs, fmt.Errorf("dismiss review %d: %w", old.ID, err))
+		}
+	}
+	return errors.Join(errs...)
+}