feat: add service list subcommand

[LiamCoop]

Summary

• Adds railway service list subcommand to list all services in a project.
• Supports --project flag to filter by project (defaulting to linked project)
• Supports --environment flag to specify environment (defaulting to linked env)
• Supports --json flag for machine-readable output

Example Output
Default

client (280794af-f5db-4f94-900c-53afafd5ecec)
Postgres (33bacc3e-80b7-4739-8473-b308bae72181)
sync-server (c8b51d04-6507-4b9a-979a-78d26083c05e)

JSON (--json)

[
  {
    "id": "280794af-f5db-4f94-900c-53afafd5ecec",
    "name": "client"
  },
  {
    "id": "33bacc3e-80b7-4739-8473-b308bae72181",
    "name": "Postgres"
  },
  {
    "id": "c8b51d04-6507-4b9a-979a-78d26083c05e",
    "name": "sync-server"
  }
]

Help (--help)

Manage services

Usage: railway service [SERVICE] [COMMAND]

Commands:
  list      List services in the current project
  link      Link a service to the current project
  status    Show deployment status for services
  logs      View logs from a service
  redeploy  Redeploy the latest deployment of a service
  restart   Restart the latest deployment of a service
  scale     Scale a service across regions
  help      Print this message or the help of the given subcommand(s)

Arguments:
  [SERVICE]  The service ID/name to link (deprecated: use 'service link' instead)

Options:
  -h, --help     Print help
  -V, --version  Print version

Test Plan

No --project flag

• railway service list w/ linked project + linked environment → lists services in that environment
• railway service list w/ no linked project → errors with No linked project found. Run railway link to connect to a project

--project flag

• railway service list --project <name> w/ --environment specified → lists services in that environment
• railway service list --project <name> w/ invalid --environment → errors with Environment not found
• railway service list --project <name> w/ no --environment, one environment in project → auto-selects it
• railway service list --project <name> w/ no --environment, multiple environments → prompts to select (interactive) or errors (non-interactive)
• railway service list --project <invalid> → errors with Project not found

Output

• railway service list --json → outputs valid JSON with service fields (id, name)
• railway service list w/ no services in environment → shows No services found
• railway service list w/ services present → shows name and ID for each service

Fixes #817