fix: dual-mode installer — works with or without sudo

Installer now detects at runtime if it can get root access:
- Root/NOPASSWD sudo: installs to system directories with systemd
- No root: installs to ~/.local/bin with @reboot cron job

Self-elevation uses 'script -qc sudo bash' for requiretty, or falls
back to user mode without hanging on password prompts.

Uninstaller checks both system and user paths.

src/Services/AgentService.php

@@ -68,7 +68,6 @@ class AgentService
 
             $output = trim($result['output']);
             $exitStatus = $result['exit_status'] ?? -1;
-            $path = '/usr/local/bin/servermanager-agent';
 
             if ($exitStatus !== 0) {
                 $lastLines = implode("\n", array_slice(explode("\n", $output), -20));
@@ -79,6 +78,11 @@ class AgentService
                 ];
             }
 
+            $path = '/usr/local/bin/servermanager-agent';
+            if (preg_match('/Binary:\s*(\S+)/', $output, $m)) {
+                $path = $m[1];
+            }
+
             $serverModel = new \ServerManager\Models\Server();
             $serverModel->setAgentInstalled($serverId, true, $path);