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.

system_discovery.py

@@ -9,6 +9,7 @@ import re
 from typing import Dict, List, Set, Optional, Any
 from datetime import datetime
 from pathlib import Path
+from command_patterns import build_ssh_command
 
 
 class SystemDiscovery:
@@ -65,12 +66,10 @@ class SystemDiscovery:
     def detect_os_type(self, hostname: str) -> str:
         """Detect the operating system of a remote host via SSH"""
         try:
-            # Use explicit SSH key path
-            ssh_key = "/var/lib/macha/.ssh/id_ed25519"
-            # Try to detect OS via SSH
+            # Use centralized command pattern - see command_patterns.py
+            ssh_cmd = build_ssh_command(hostname, "cat /etc/os-release", timeout=10)
             result = subprocess.run(
-                ["ssh", "-i", ssh_key, "-o", "ConnectTimeout=5", "-o", "StrictHostKeyChecking=no",
-                 hostname, "cat /etc/os-release"],
+                ssh_cmd,
                 capture_output=True,
                 text=True,
                 timeout=10
@@ -96,9 +95,9 @@ class SystemDiscovery:
                     return 'alpine'
             
             # Try uname for other systems
+            ssh_cmd = build_ssh_command(hostname, "uname -s", timeout=10)
             result = subprocess.run(
-                ["ssh", "-i", ssh_key, "-o", "ConnectTimeout=5", "-o", "StrictHostKeyChecking=no",
-                 hostname, "uname -s"],
+                ssh_cmd,
                 capture_output=True,
                 text=True,
                 timeout=10