Add multi-deployment comparison mode

[lowhung]

Summary

Support connecting to and comparing multiple Caryatid deployments simultaneously.

Configuration

[deployments]
"production" = { url = "amqp://prod.example.com", exchange = "caryatid" }
"staging" = { url = "amqp://staging.example.com", exchange = "caryatid" }
"development" = { url = "amqp://localhost", exchange = "caryatid" }

[comparison]
show_comparison_panel = true
highlight_threshold = 0.2  # 20% difference triggers highlighting

UI Features

• Tabs for different deployments
• Side-by-side graph comparison view
• Diff highlighting (showing which modules differ)
• Correlation analysis (same module across environments)
• Regression detection (performance degradation in newer deployment)

Benefits

• Compare staging vs production behavior
• Validate deployments before promotion
• Debug environment-specific issues