Legacy compatibility wrapper for cloud/provider operations.

• Deprecated command.
• Canonical replacement: nself infra provider ...

• nself cloud provider list -> nself infra provider list
• nself cloud provider init <name> -> nself infra provider init <name>
• nself cloud provider validate -> nself infra provider validate
• nself cloud provider info <name> -> nself infra provider show <name>
• nself cloud server create -> nself infra provider server create
• nself cloud server list -> nself infra provider server list
• nself cloud server ssh <name> -> nself infra provider server ssh <name>
• nself cloud cost estimate -> nself infra provider cost estimate
• nself cloud deploy quick <server> -> nself infra provider deploy quick <server>

nself cloud <legacy-subcommand> ...

• Canonical command: PROVIDER.md
• Infra namespace: INFRA.md