Fix DoltHub fork auth and surface join errors to stderr

Add authorization header for DoltHub GraphQL API (was only sending
cookie). Print join errors to stderr so they're visible with cobra's
SilenceErrors enabled.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: julianknutsen

cmd/wl/cmd_join.go

@@ -150,7 +150,8 @@ func runJoin(stdout, stderr io.Writer, upstream, handle, displayName, email, for
 	fmt.Fprintf(stdout, "Joining wasteland %s (fork to %s/%s)...\n", upstream, forkOrg, dbName)
 	cfg, err := svc.Join(upstream, forkOrg, handle, displayName, email, wlVersion)
 	if err != nil {
-		return err
+		fmt.Fprintf(stderr, "wl join: %v\n", err)
+		return errExit
 	}
 
 	fmt.Fprintf(stdout, "\n%s Joined wasteland: %s\n", style.Bold.Render("✓"), upstream)

internal/remote/dolthub.go

@@ -68,6 +68,7 @@ func (d *DoltHubProvider) Fork(fromOrg, fromDB, toOrg string) error {
 		return fmt.Errorf("creating fork request: %w", err)
 	}
 	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("authorization", "token "+d.token)
 	req.Header.Set("Cookie", "dolthubToken="+d.token)
 
 	client := &http.Client{Timeout: 60 * time.Second}

internal/remote/dolthub_test.go

@@ -27,10 +27,9 @@ func TestDoltHubProvider_Fork(t *testing.T) {
 					t.Errorf("expected POST, got %s", r.Method)
 				}
 
-				// Verify cookie auth.
-				cookie := r.Header.Get("Cookie")
-				if !strings.Contains(cookie, "dolthubToken=test-token") {
-					t.Errorf("expected dolthubToken cookie, got %q", cookie)
+				// Verify auth header.
+				if r.Header.Get("authorization") != "token test-token" {
+					t.Errorf("expected auth header, got %q", r.Header.Get("authorization"))
 				}
 
 				// Verify GraphQL request body.