Add bundle debug list-targets command

[pavloKozlov]

Why

Provide a lightweight way to retrieve bundle target names along with their default, mode, and workspace.host fields. This is a prerequisite for running other bundle CLI commands (deploy, validate, run, etc.), which all require --target.

Changes

Adds a new hidden bundle debug list-targets subcommand that loads only the local YAML configuration (bundle.MustLoad + phases.Load) and returns each target's name, default, mode, and workspace.host. No target selection, no variable resolution, no authentication, no API calls.

Text output:
dev (default) development https://dev.example.com
prod production https://prod.example.com
staging https://staging.example.com

JSON output:

  {
    "targets": [
      {"name": "dev", "default": true, "mode": "development", "host": "https://dev.example.com"},
      {"name": "prod", "mode": "production", "host": "https://prod.example.com"},
      {"name": "staging", "host": "https://staging.example.com"}
    ]
  }

Test plan

• Unit tests for collectTargets (sorting, all fields, nil workspace, empty map)
• Acceptance test covering text and JSON output
• Command is hidden from bundle debug --help