Make dashboard updateable

cache.go

@@ -138,6 +138,28 @@ func (c *CachedGitHubService) ReplyToThread(
 	return writer.ReplyToThread(ctx, threadID, body)
 }
 
+func (c *CachedGitHubService) UpdatePullRequest(
+	ctx context.Context,
+	pullRequestID string,
+	update PullRequestMetadata,
+) (PullRequestMetadata, error) {
+	writer, ok := c.remote.(GitHubPullRequestWriteService)
+	if !ok {
+		return PullRequestMetadata{}, errors.New("GitHub service does not support pull request updates")
+	}
+	return writer.UpdatePullRequest(ctx, pullRequestID, update)
+}
+
+func (c *CachedGitHubService) ListBranches(
+	ctx context.Context, owner, repo string,
+) ([]RepositoryBranch, error) {
+	service, ok := c.remote.(GitHubBranchService)
+	if !ok {
+		return nil, errors.New("GitHub service does not support listing branches")
+	}
+	return service.ListBranches(ctx, owner, repo)
+}
+
 func (c *CachedGitHubService) pullRequestsKey(owner, repo string, limit int, showAll bool) string {
 	return fmt.Sprintf("prs:%s/%s:%d:%t", owner, repo, limit, showAll)
 }