Introduce picard-cli as the unified command-line interface for Picard, replacing the standalone picard-plugins command with modern verb-style subcommands.
  
Motivation:
  

• picard-plugins uses GNU-style --flag options which are hard to discover and don't scale to multiple CLI tools (profiles, config, etc.)
• Having separate entry points (picard-plugins, potentially picard-profiles, etc.) leads to duplicated bootstrap code
• Verb-style subcommands (picard-cli plugins install, picard-cli plugins list) are more discoverable and match modern CLI conventions (git, docker, cargo, gh)