Task: add --json output for server commands

[mother-6000]

Summary

Implement formatted JSON output for the scoped ReductStore CLI command group when the global --json flag is set.

Scope

• server alive
• server status
• server license

Definition of done

• The scoped commands preserve their current human-readable output when --json is not set.
• The scoped commands emit valid pretty/formatted JSON when --json is set.
• JSON field names are stable, descriptive, and suitable for automation.
• Existing command behavior, validation, and exit codes are preserved.
• Tests cover representative JSON output for the scoped commands.
• Documentation or examples are updated if user-facing behavior needs clarification.

Links

Parent feature: #250

Notes

• Keep cp out of scope for this JSON output feature.
• Prefer shared output helpers so command groups stay consistent.