🔒 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/Data/LittleShopContext.cs

@@ -28,6 +28,7 @@ public class LittleShopContext : DbContext
     public DbSet<PushSubscription> PushSubscriptions { get; set; }
     public DbSet<Review> Reviews { get; set; }
     public DbSet<BotContact> BotContacts { get; set; }
+    public DbSet<SystemSetting> SystemSettings { get; set; }
 
     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {
@@ -302,5 +303,12 @@ public class LittleShopContext : DbContext
             entity.HasIndex(e => new { e.ProductId, e.IsApproved, e.IsActive });
             entity.HasIndex(e => new { e.CustomerId, e.ProductId }).IsUnique(); // One review per customer per product
         });
+
+        // SystemSetting entity
+        modelBuilder.Entity<SystemSetting>(entity =>
+        {
+            entity.HasKey(e => e.Key);
+            entity.HasIndex(e => e.Key).IsUnique();
+        });
     }
 }