kiro: use q.<region>.amazonaws.com for ListModels (same as kiro-cli)

The management.*.kiro.dev endpoint was slower/less reliable. Switch to
the same q.<region>.amazonaws.com endpoint that kiro-cli uses, deriving
the region from the profile ARN or runtime endpoint.

pkg/backend/codewhisperer_internal.go

@@ -603,6 +603,28 @@ func kiroEndpointForRegion(region string) string {
 	return "https://runtime." + strings.TrimSpace(region) + ".kiro.dev/"
 }
 
+// kiroListModelsEndpoint derives the q.<region>.amazonaws.com endpoint for ListModels.
+// Falls back to the management endpoint if region cannot be determined.
+func kiroListModelsEndpoint(runtimeEndpoint, profileARN string) string {
+	// Try to extract region from profile ARN (arn:aws:codewhisperer:<region>:...)
+	if parts := strings.Split(profileARN, ":"); len(parts) >= 4 && parts[3] != "" {
+		return "https://q." + parts[3] + ".amazonaws.com/"
+	}
+	// Try to extract region from runtime endpoint (runtime.<region>.kiro.dev)
+	host := strings.TrimPrefix(strings.TrimPrefix(runtimeEndpoint, "https://"), "http://")
+	host = strings.TrimSuffix(host, "/")
+	if strings.HasPrefix(host, "runtime.") && strings.HasSuffix(host, ".kiro.dev") {
+		region := strings.TrimPrefix(host, "runtime.")
+		region = strings.TrimSuffix(region, ".kiro.dev")
+		return "https://q." + region + ".amazonaws.com/"
+	}
+	// Fallback: use management endpoint
+	if mgmt, err := kiroManagementEndpointFor(runtimeEndpoint); err == nil {
+		return mgmt
+	}
+	return runtimeEndpoint
+}
+
 func kiroManagementEndpointFor(endpoint string) (string, error) {
 	parsed, err := url.Parse(strings.TrimSpace(endpoint))
 	if err != nil {
@@ -727,15 +749,12 @@ func (c *kiroAPIClient) ListModels(ctx context.Context, profileARN string) (*kir
 	if err != nil {
 		return nil, err
 	}
-	// ListModels uses the management endpoint (management.*.kiro.dev) rather
-	// than the streaming endpoint (runtime.*.kiro.dev).
-	mgmtEndpoint, err := kiroManagementEndpointFor(c.endpoint)
+	// Use q.<region>.amazonaws.com (same as kiro-cli) rather than
+	// management.*.kiro.dev which is slower/less reliable.
+	listEndpoint := kiroListModelsEndpoint(c.endpoint, profileARN)
+	targetURL, err := url.Parse(listEndpoint)
 	if err != nil {
-		mgmtEndpoint = c.endpoint // fall back to streaming endpoint
-	}
-	targetURL, err := url.Parse(mgmtEndpoint)
-	if err != nil {
-		return nil, fmt.Errorf("parse management endpoint: %w", err)
+		return nil, fmt.Errorf("parse list models endpoint: %w", err)
 	}
 	query := targetURL.Query()
 	query.Set("origin", kiroDefaultOrigin)