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.

remote_monitor.py

@@ -7,6 +7,7 @@ import json
 import subprocess
 from typing import Dict, Any, Optional
 from pathlib import Path
+from command_patterns import build_ssh_command
 
 
 class RemoteMonitor:
@@ -36,16 +37,8 @@ class RemoteMonitor:
             (success, stdout, stderr)
         """
         try:
-            # Use explicit SSH key path from macha user's home directory
-            ssh_key = "/var/lib/macha/.ssh/id_ed25519"
-            ssh_cmd = [
-                "ssh",
-                "-i", ssh_key,
-                "-o", "StrictHostKeyChecking=no",
-                "-o", "ConnectTimeout=10",
-                self.ssh_target,
-                command
-            ]
+            # Use centralized command pattern - see command_patterns.py
+            ssh_cmd = build_ssh_command(self.hostname, command, timeout)
             
             result = subprocess.run(
                 ssh_cmd,