refactor(ulhost): rewrite product to follow uhost pattern

Restructure the ulhost product to mirror the uhost product layout:
- Split each command into its own file (create/list/delete/start/stop/
  restart/poweroff/reset-password/reinstall-os/modify-attribute/bundles/price)
- Add internal/image subpackage with list command
- Add completion.go, rows.go, status.go, describe.go helpers
- Add testdata goldens (cmdtree + completion)

Fix BindGroup incompatibility: the ucompshare DescribeULHostInstanceRequest
has no Tag field, so the --group binding is dropped from ulhost list.

Note backend API operations not yet exposed (UpdateULHostInstanceFirewall,
ModifyULHostProxyIp, CheckULHostResourceCapacity, share-bandwidth, openclaw)
are documented in cmd.go — the public ucompshare SDK does not support them.