Refactor Flow Lens as a Salesforce CLI Plugin

# Refactor Flow Lens as a Salesforce CLI Plugin

## Description
Convert Flow Lens from a standalone Deno executable into a Salesforce CLI (`sf`) plugin to better integrate with the Salesforce development ecosystem and improve developer experience.

## Proposed Changes

### 1. Command Structure
```bash
sf flow-lens:visualize --flow-names --format
sf flow-lens:diff --from --to
```

### 2. Core Changes Required
1. Port from Deno to Node.js environment
2. Implement Salesforce CLI plugin architecture
3. Update documentation and examples

## Benefits
1. Seamless integration with Salesforce development workflow
2. One-command installation via `sf plugins install`
3. Consistent experience with other Salesforce tools
5. Better CI/CD integration

## Technical Requirements
- Node.js 18.x or later
- Salesforce CLI v2

## Implementation Notes
- Maintain existing diagram generation logic
- Follow Salesforce CLI plugin best practices