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

[denik]

for fields that have variable in default and mode, should we record behaviour as well in the test? (even if it does not work, it's good to know what happens and that it degrades gracefully).

[pavloKozlov]

Updated.

[denik]

these tests seem redundant given that we have acceptance test

[pavloKozlov]

Removed these tests in favour of acceptance tests.