fix: ensure all tool responses are JSON-serializable

[oheckmann74]

Summary

Several MCP tool handlers return { toolResult: ... } which doesn't properly serialize the response. This causes tools like list_group_testers to return [object Object] instead of actual tester data.

Problem

When calling list_group_testers, the MCP client receives:

[object Object]

Instead of the actual tester data array.

Root Cause

The list_apps and get_app_info handlers use formatResponse():

case "list_apps":
  const appsData = await this.appHandlers.listApps(args as any);
  return formatResponse(appsData);  // ✓ Works correctly

But most other handlers return raw objects:

case "list_group_testers":
  return { toolResult: await this.betaHandlers.listGroupTesters(args as any) };  // ✗ Broken

Solution

Changed all affected handlers to use formatResponse() which wraps responses in the proper MCP content format with JSON.stringify().

Affected Tools

• list_beta_groups
• list_group_testers
• add_tester_to_group
• remove_tester_from_group
• create_app_store_version
• list_app_store_versions
• list_app_store_version_localizations
• get_app_store_version_localization
• update_app_store_version_localization
• create_bundle_id
• list_bundle_ids
• get_bundle_id_info
• enable_bundle_capability
• disable_bundle_capability
• list_devices
• list_users
• create_analytics_report_request
• list_analytics_reports
• list_analytics_report_segments
• download_analytics_report_segment
• download_sales_report
• download_finance_report
• list_schemes

Test Plan

• Build succeeds (npm run build)
• Call list_group_testers with a valid group ID
• Verify response contains actual tester data (names, emails, IDs)
• Verify other affected tools also return properly formatted JSON