feat: Add plugin architecture for extensibility

[anjor]

Feature Request: Plugin Architecture

Overview

Implement a plugin system that allows third-party developers to extend pltr-cli with custom commands, authentication methods, and data formatters.

Proposed Implementation

• Plugin Discovery: Automatic discovery of plugins in ~/.config/pltr/plugins/
• Plugin Types:
  • Command Plugins: Add new command groups (pltr myplugin command)
  • Auth Plugins: Custom authentication methods
  • Formatter Plugins: New output formats beyond table/json/csv
  • Service Plugins: Wrapper for additional Foundry APIs
• Plugin API: Well-defined interfaces for plugin development
• Plugin Management: pltr plugin list|install|enable|disable|remove

Plugin Structure

~/.config/pltr/plugins/
├── my_plugin/
│   ├── plugin.json          # Metadata and configuration
│   ├── __init__.py         # Plugin entry point
│   ├── commands.py         # Custom commands
│   ├── auth.py            # Custom auth (optional)
│   └── formatters.py      # Custom formatters (optional)

Plugin API

• Base Classes: BaseCommand, BaseAuth, BaseFormatter, BaseService
• Registration: Plugins register via decorators or metadata
• Lifecycle Hooks: plugin_init, plugin_activate, plugin_deactivate
• Configuration: Access to pltr config and profiles
• Error Handling: Isolated plugin failures don't crash CLI

Use Cases

• Custom Data Sources: Plugins for non-Foundry APIs
• Specialized Formatters: Export to Excel, PowerBI, Tableau formats
• Domain-Specific Commands: Industry-specific data operations
• Integration Tools: Slack/Teams notifications, Jira integration
• Development Tools: Test data generation, mock services

Technical Requirements

• Plugin isolation and sandboxing
• Version compatibility checking
• Plugin dependency management
• Security review process for official plugins
• Comprehensive plugin development documentation

Acceptance Criteria

• Plugin discovery and loading system functional
• Example plugins demonstrating each plugin type
• Plugin management commands operational
• Plugin development documentation complete
• Security isolation prevents malicious plugins
• Plugin API stability guarantees established
• Comprehensive test coverage including plugin system

Priority: Low
Labels: enhancement, architecture, Phase-8
Effort: Large