[FEATURE] Implement cx save/restore workspace snapshots

[mikejmorgan-ai]

Summary

The cx save, cx restore, and cx snapshots commands have stub implementations. These need full implementation for workspace state persistence.

Current State

// snapshot.rs - stubs only
println!("cx save: Workspace snapshots not yet implemented");
println!("cx restore: Workspace snapshots not yet implemented");
println!("cx snapshots: Workspace snapshots not yet implemented");

Required Functionality

cx save [name]

• Capture current terminal state (tabs, panes, working directories)
• Save to ~/.cx/snapshots/<name>.json
• Auto-generate name if not provided (e.g., myproject-0201)

cx restore

• Read snapshot JSON
• Recreate terminal layout
• Restore working directories
• Optionally re-run last commands

cx snapshots

• --list - List all saved snapshots
• --delete <name> - Remove a snapshot
• --info <name> - Show snapshot details

Snapshot Format

{
  "name": "myproject-0201",
  "created": "2026-02-01T12:00:00Z",
  "tabs": [
    {
      "title": "main",
      "panes": [
        {"cwd": "/home/user/project", "last_command": "npm run dev"}
      ]
    }
  ]
}

Acceptance Criteria

• cx save creates valid JSON snapshot
• cx restore recreates workspace layout
• cx snapshots --list works
• Unit tests for save/restore logic
• Integration with WezTerm mux system
• BSL 1.1 header in source files