Fix: Always use explicit SSH key path for all SSH operations

CRITICAL FIX: SSH keys were not being auto-loaded, causing connection failures.

Changes:
- tools.py: SSH commands now include -i /var/lib/macha/.ssh/id_ed25519
- remote_monitor.py: Use explicit key path instead of sudo ssh
- system_discovery.py: Added explicit key path to all SSH calls
- system_prompt.txt: Document automatic SSH key loading
- DESIGN.md: Clarify CRITICAL requirement for explicit key paths

All SSH operations now explicitly specify:
  -i /var/lib/macha/.ssh/id_ed25519 -o StrictHostKeyChecking=no

This ensures Macha can reliably connect to remote hosts without
depending on SSH agent or automatic key discovery.

tools.py

@@ -269,17 +269,20 @@ class SysadminTools:
                 }
         
         # Automatically configure SSH commands to use macha user on remote systems
-        # Transform: ssh hostname cmd -> ssh macha@hostname sudo cmd
+        # Transform: ssh hostname cmd -> ssh -i /var/lib/macha/.ssh/id_ed25519 macha@hostname sudo cmd
         if command.strip().startswith('ssh ') and '@' not in command.split()[1]:
             parts = command.split(maxsplit=2)
             if len(parts) >= 2:
                 hostname = parts[1]
                 remaining = ' '.join(parts[2:]) if len(parts) > 2 else ''
+                # Always use explicit SSH key path
+                ssh_key = "/var/lib/macha/.ssh/id_ed25519"
+                ssh_opts = f"-i {ssh_key} -o StrictHostKeyChecking=no"
                 # If there's a command to run remotely, prefix it with sudo
                 if remaining:
-                    command = f"ssh macha@{hostname} sudo {remaining}".strip()
+                    command = f"ssh {ssh_opts} macha@{hostname} sudo {remaining}".strip()
                 else:
-                    command = f"ssh macha@{hostname}".strip()
+                    command = f"ssh {ssh_opts} macha@{hostname}".strip()
         
         try:
             result = subprocess.run(