feat: validate required SSH permissions before creating server

- New server_permissions table (migration 007) stores required SSH permissions per server
- PermissionValidator service connects via SSH and validates each permission before save
- ServerPermission model for CRUD on server_permissions table
- Web flow: create/edit forms include dynamic permission rows with quick-add presets
- API flow: serverAdd/serverUpdate accept permissions array, return 400 on failure
- Show view displays required permissions on server detail page
- Form input preserved on validation failure (credentials excluded)
- AGENTS.md updated with new conventions

src/Models/ServerPermission.php

@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+
+namespace ServerManager\Models;
+
+use ServerManager\Core\Database;
+
+class ServerPermission
+{
+    private Database $db;
+
+    public function __construct()
+    {
+        $this->db = Database::getInstance();
+    }
+
+    public function save(int $serverId, array $permissions): void
+    {
+        $this->deleteByServerId($serverId);
+
+        foreach ($permissions as $perm) {
+            if (empty($perm['type']) || !isset($perm['value'])) {
+                continue;
+            }
+
+            $this->db->insert('server_permissions', [
+                'server_id' => $serverId,
+                'permission_type' => $perm['type'],
+                'permission_value' => $perm['value'],
+                'description' => $perm['description'] ?? null,
+                'created_at' => date('Y-m-d H:i:s'),
+            ]);
+        }
+    }
+
+    public function getByServerId(int $serverId): array
+    {
+        return $this->db->fetchAll(
+            'SELECT * FROM server_permissions WHERE server_id = ? ORDER BY id ASC',
+            [$serverId]
+        );
+    }
+
+    public function deleteByServerId(int $serverId): void
+    {
+        $this->db->delete('server_permissions', 'server_id = ?', [$serverId]);
+    }
+
+    public static function formatForValidation(array $permissions): array
+    {
+        return array_map(fn($p) => [
+            'type' => $p['permission_type'],
+            'value' => $p['permission_value'],
+            'description' => $p['description'] ?? '',
+        ], $permissions);
+    }
+}