Refactor CLI into modular command files

[Tom-Camp]

📝 One-line Summary

Moves the Click commands from cli to /commands and the function from allusgov.py to the individual command files.

Issue: #1234 (if applicable)

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📖 Description

• Extracted all Click commands from cli.py into dedicated modules under commands/.
• Kept the public CLI surface unchanged; command names, options, and behavior remain the same.
• cli.py now only defines the root Click group and registers commands from commands/.
• This makes it easier to:
  • Add new commands without touching a large cli.py or allusgov.py.
  • Maintain and test each command in isolation.
  • Share business logic between commands via regular Python modules instead of one large file.

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🔧 Type of Change

Indicate all that apply:

• 🆕 New feature (adds new functionality)
• 🐛 Bug fix (non-breaking fix for a known issue)
• 🔧 Configuration change
• ♻️ Code refactor / performance improvement
• 📝 Documentation or non-code contribution

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✅ Tasks to Complete

Checklist of work being delivered in this PR:

• Add/modify feature logic
• Write or update documentation
• Add or update tests
• Accessibility review
• Internal stakeholder check-in

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👀 Review Checklist

For reviewers to verify before approving:

• Code follows project conventions
• Documentation is clear and complete
• Tests added or updated
• CHANGELOG updated (if applicable)
• No major accessibility regressions

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🚀 Deployment Notes

Are there migrations, feature flags, config updates, or coordination steps required?