feat: Add --exclude option for host exclusion (pdsh -x compatibility)

[inureyes]

Summary

Add a new --exclude option to bssh that allows users to exclude specific hosts from the target list. This is part of pdsh compatibility mode (Phase 1 of #91).

Changes

CLI Option

• Added --exclude option with comma-separated value support
• Supports wildcard patterns using glob matching (e.g., db*, *-backup)
• Applied after --filter option for precise control

Usage Examples

# Exclude single host
bssh -H "node1,node2,node3" --exclude "node2" "uptime"

# Exclude multiple hosts
bssh -C production --exclude "web1,web2" "apt update"

# Exclude with wildcard pattern
bssh -C production --exclude "db*" "systemctl restart"

# Exclude backup nodes
bssh -C production --exclude "*-backup" "df -h"

Implementation Details

• New exclude_nodes() function in src/app/nodes.rs
• Security validations for pattern length, wildcard count, and character restrictions
• Integration with existing node resolution workflow
• 17 comprehensive unit tests covering various scenarios

Note

Short option -x is not used due to conflict with existing --no-x11 option. The -x short form will be available in pdsh compatibility mode.

Test Plan

• All 619 existing tests pass
• New unit tests for exclusion logic pass
• Clippy checks pass with no warnings
• Build succeeds
• Help text displays correctly

Closes #93