🔒 SECURITY: Emergency fixes and hardening

EMERGENCY FIXES:
✅ DELETE MockSilverPayService.cs - removed fake payment system
✅ REMOVE mock service registration - no fake payments possible
✅ GENERATE new JWT secret - replaced hardcoded key
✅ FIX HttpClient disposal - proper resource management

SECURITY HARDENING:
✅ ADD production guards - prevent mock services in production
✅ CREATE environment configs - separate dev/prod settings
✅ ADD config validation - fail fast on misconfiguration

IMPACT:
- Mock payment system completely eliminated
- JWT authentication now uses secure keys
- Production deployment now validated on startup
- Resource leaks fixed in TeleBot currency API

🤖 Generated with [Claude Code](https://claude.ai/code)

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

LittleShop/Areas/Admin/Views/Shared/_Layout.cshtml

@@ -92,6 +92,11 @@
                                 <i class="fas fa-robot"></i> Bots
                             </a>
                         </li>
+                        <li class="nav-item">
+                            <a class="nav-link" href="@Url.Action("Index", "SystemSettings", new { area = "Admin" })">
+                                <i class="fas fa-cog"></i> Settings
+                            </a>
+                        </li>
                     </ul>
                     <ul class="navbar-nav">
                         <li class="nav-item dropdown">