🔒 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/SilverPayService.cs

@@ -215,6 +215,35 @@ public class SilverPayService : ISilverPayService
         }
     }
 
+    public async Task<List<string>> GetSupportedCurrenciesAsync()
+    {
+        try
+        {
+            var response = await _httpClient.GetAsync("/api/v1/currencies");
+
+            if (!response.IsSuccessStatusCode)
+            {
+                _logger.LogWarning("Failed to get supported currencies from SilverPAY. Status: {Status}", response.StatusCode);
+                // Return a default list of commonly supported currencies
+                return new List<string> { "BTC", "ETH", "USDT", "LTC" };
+            }
+
+            var json = await response.Content.ReadAsStringAsync();
+            var currencies = JsonSerializer.Deserialize<List<string>>(json, new JsonSerializerOptions
+            {
+                PropertyNameCaseInsensitive = true
+            });
+
+            return currencies ?? new List<string> { "BTC" };
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Error getting supported currencies from SilverPAY");
+            // Return a safe default
+            return new List<string> { "BTC" };
+        }
+    }
+
     private static string GetSilverPayCurrency(CryptoCurrency currency)
     {
         return currency switch