fix: add mass assignment protection to models

Replace $guarded = [] with explicit $fillable whitelists across all
models. Update controllers to use request->only($allowedFields) when
assigning request data. Switch Livewire components to forceFill() for
explicit mass assignment. Add integration tests for mass assignment
protection.

app/Models/StandalonePostgresql.php

@@ -13,7 +13,34 @@ 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',
+    ];
 
     protected $appends = ['internal_db_url', 'external_db_url', 'database_type', 'server_status'];