Refactor: Centralize command patterns in single source of truth

CRITICAL: Prevents inconsistent sudo/SSH patterns across codebase.

Created command_patterns.py with:
- Single source of truth for ALL command execution patterns
- SSH key path constant: /var/lib/macha/.ssh/id_ed25519
- Remote user constant: macha
- sudo prefix for all remote commands
- Helper functions: build_ssh_command(), transform_ssh_command()
- Self-validation tests

Updated files to use centralized patterns:
- tools.py: Uses transform_ssh_command()
- remote_monitor.py: Uses build_ssh_command()
- system_discovery.py: Uses build_ssh_command()
- DESIGN.md: Documents centralized approach

Benefits:
- Impossible to have inconsistent patterns
- Single place to update if needed
- Self-documenting with validation tests
- Prevents future refactoring errors

DO NOT duplicate these patterns in other files - always import.

DESIGN.md

@@ -26,9 +26,12 @@ Macha is an AI-powered autonomous system administrator capable of monitoring, ma
 **Macha CAN and SHOULD use SSH to manage other hosts.**
 
 #### SSH Access
-- **CRITICAL**: Always uses explicit SSH key path: `-i /var/lib/macha/.ssh/id_ed25519`
+- **CRITICAL**: All command patterns defined in `command_patterns.py` (SINGLE SOURCE OF TRUTH)
+- Always uses explicit SSH key path: `-i /var/lib/macha/.ssh/id_ed25519`
 - All SSH commands automatically include the `-i` flag with absolute key path
+- Remote commands always prefixed with `sudo`
 - Runs as `macha` user (UID 2501)
+- **DO NOT DUPLICATE these patterns elsewhere** - import from `command_patterns.py`
 - Has `NOPASSWD` sudo access for administrative commands
 - Shares SSH keys with other hosts in the infrastructure
 - Can SSH to: `rhiannon`, `alexander`, `UCAR-Kinston`, and others in the flake