🔒 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/Services/AuthService.cs

@@ -171,7 +171,7 @@ public class AuthService : IAuthService
 
     private string GenerateJwtToken(User user)
     {
-        var jwtKey = _configuration["Jwt:Key"] ?? "ThisIsASuperSecretKeyForJWTAuthenticationThatIsDefinitelyLongerThan32Characters!";
+        var jwtKey = _configuration["Jwt:Key"] ?? throw new InvalidOperationException("JWT Key not configured. Set Jwt:Key in appsettings.json");
         var jwtIssuer = _configuration["Jwt:Issuer"] ?? "LittleShop";
         var jwtAudience = _configuration["Jwt:Audience"] ?? "LittleShop";