fix: cancel in-flight GetCircularDependencies request when GetGraph fails

Derive a cancellable context at the top of fetchGraphWithCircularDeps and
use defer cancel() so that the in-flight HTTP request to the circular-
dependencies API endpoint is aborted as soon as GetGraph returns an error,
avoiding wasted network bandwidth and API quota.

Fixes #78

Co-Authored-By: Grey Newell <greyshipscode@gmail.com>
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: claude[bot] <claude[bot]@users.noreply.github.com>

Author: 4 people

cmd/run.go

@@ -268,6 +268,9 @@ func fetchGraphWithCircularDeps(
 	repoZip []byte,
 	logFn func(string, ...interface{}),
 ) (*api.ProjectGraph, error) {
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
 	type graphResult struct {
 		graph *api.ProjectGraph
 		err   error