Add marr sync command to propagate standards between projects

[virtualian]

Summary

• Add marr sync command for propagating standards between MARR-configured projects
• Add project registry at ~/.claude/marr/projects.json
• Auto-register projects on marr init --project
• Auto-regenerate trigger tables after syncing
• Remove marr standard sync (functionality folded into marr sync)

Usage

# Interactive mode - prompts for source and targets
marr sync

# Explicit source and target
marr sync --from ~/projects/marr --to ~/projects/npm-scanner

# Preview changes
marr sync --dry-run

# Manage registry
marr sync --register      # Add current project
marr sync --unregister    # Remove current project
marr sync --list          # Show registered projects

Closes #37

Test plan

• Build passes
• All 49 tests pass
• marr sync --help shows correct usage
• marr sync --register adds project to registry
• marr sync --list shows registered projects
• Manual testing of sync between projects