Fix: Add --provider Option to CLI Commands

[salmanabdurrahman]

Summary

This PR adds the --provider (-p) option to:

• guardian workflow
• guardian recon
• guardian scan

Users can now override the AI provider directly from the command line without editing guardian.yaml.

Fixes #13

Changes

• Added --provider / -p flag
• Provider validation (gemini, openai, claude, openrouter)
• Clear error message for invalid providers
• Fully backward compatible (works without the flag)

Files updated:

• workflow.py
• recon.py
• scan.py
  Total: 3 files, +56 insertions

Example Usage

guardian workflow run --name recon --target example.com --provider gemini
guardian recon --domain example.com --provider claude
guardian scan --target 192.168.1.1 --provider openai

Testing

• Option appears in help text
• Provider validation works
• Override functions correctly
• No breaking changes

This keeps consistency with the existing --model option and improves usability.