feat!: restructure CLI from dd-search to ddog with domain-first commands

[tmcinerney]

Summary

Restructures the CLI from a flat command structure to a strict domain-first pattern (GitHub-style) and renames the binary from dd-search to ddog. This provides better organization and scalability for future features.

Changes

Breaking Changes

• Command structure: Changed from flat commands to domain/action hierarchy
  • dd-search logs → ddog logs search
  • dd-search spans → ddog spans search
  • dd-search metrics → ddog metrics query
  • dd-search list-metrics → ddog metrics list
• Binary name: Renamed from dd-search to ddog

Features

• Created shared CLI components (TimeRange, Pagination) for DRY code reuse
• Organized CLI into modular domain-based structure:
  • src/cli/args.rs - Main CLI and domain enum
  • src/cli/shared.rs - Reusable argument structures
  • src/cli/logs.rs, spans.rs, metrics.rs - Domain-specific actions
• Reorganized command implementations into domain subdirectories
• Updated all documentation, GitHub workflows, and release artifacts

Impact

• 23 files changed: 307 insertions(+), 361 deletions(-)
• Affected areas: CLI interface, command routing, documentation, CI/CD
• Future extensibility: Easy to add new domains (monitors, dashboards) and actions

Testing

• ✅ All unit tests pass (26 library + 18 binary tests)
• ✅ Build succeeds for new binary name
• ✅ Pre-commit hooks pass (formatting, clippy, tests)