refactor: define explicit fillable attributes on all Eloquent models

Replace $guarded usage with explicit $fillable arrays across all models.
Sync fillable definitions with current database schema and add tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Models/StandalonePostgresql.php

@@ -13,7 +13,40 @@ class StandalonePostgresql extends BaseModel
 {
     use ClearsGlobalSearchCache, HasFactory, HasMetrics, HasSafeStringAttribute, SoftDeletes;
 
-    protected $guarded = [];
+    protected $fillable = [
+        'name',
+        'description',
+        'postgres_user',
+        'postgres_password',
+        'postgres_db',
+        'postgres_initdb_args',
+        'postgres_host_auth_method',
+        'postgres_conf',
+        'init_scripts',
+        'status',
+        'image',
+        'is_public',
+        'public_port',
+        'ports_mappings',
+        'limits_memory',
+        'limits_memory_swap',
+        'limits_memory_swappiness',
+        'limits_memory_reservation',
+        'limits_cpus',
+        'limits_cpuset',
+        'limits_cpu_shares',
+        'started_at',
+        'restart_count',
+        'last_restart_at',
+        'last_restart_type',
+        'last_online_at',
+        'public_port_timeout',
+        'enable_ssl',
+        'ssl_mode',
+        'is_log_drain_enabled',
+        'is_include_timestamps',
+        'custom_docker_run_options',
+    ];
 
     protected $appends = ['internal_db_url', 'external_db_url', 'database_type', 'server_status'];