Draft: Add gdk org replication-status command

What does this merge request do and why?

Part of gitlab#571916 (closed)

Adds a new gdk org replication-status command to check Geo replication status for organization migration between cells.

Usage

# Check replication status
gdk org replication-status

# Wait for replication to complete (useful in scripts)
gdk org replication-status --wait --timeout 600

This requires org_migration.target_cell to be configured in your gdk.yml.

New files

• lib/gdk/command/org.rb - Command handler
• lib/org_manager.rb - Replication status logic
• spec/lib/gdk/command/org_spec.rb - Command tests
• spec/lib/org_manager_spec.rb - OrgManager tests

Related MRs

This is the first in a series of MRs to support organization migration:

1. This MR - replication-status command (foundation)
2. !5677 - configure-replication command
3. More commands to follow (start-replication, cutover, etc.)

Full POC with all commands: !5555

How to set up and validate locally

1. Configure a cell with Geo enabled:

   org_migration:
     target_cell: protocell
   geo:
     enabled: true

2. Run gdk org replication-status

Merge request checklist

• This MR references an issue describing the change.
• This change is backward compatible.
• Tests added for new functionality.
• Documentation added/updated.