Remove BTCPay completely, integrate SilverPAY only, configure TeleBot with real token

- Removed all BTCPay references from services and configuration
- Implemented SilverPAY as sole payment provider (no fallback)
- Fixed JWT authentication with proper key length (256+ bits)
- Added UsersController with full CRUD operations
- Updated User model with Email and Role properties
- Configured TeleBot with real Telegram bot token
- Fixed launchSettings.json with JWT environment variable
- E2E tests passing for authentication, catalog, orders
- Payment creation pending SilverPAY server fix

🤖 Generated with Claude Code

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

LittleShop/appsettings.json

@@ -3,16 +3,17 @@
     "DefaultConnection": "Data Source=littleshop.db"
   },
   "Jwt": {
-    "Key": "YourSuperSecretKeyThatIsAtLeast32CharactersLong!",
+    "Key": "ThisIsASuperSecretKeyForJWTAuthenticationThatIsDefinitelyLongerThan32Characters!",
     "Issuer": "LittleShop",
     "Audience": "LittleShop",
     "ExpiryInHours": 24
   },
-  "BTCPayServer": {
-    "BaseUrl": "https://pay.silverlabs.uk",
-    "ApiKey": "994589c8b514531f867dd24c83a02b6381a5f4a2",
-    "StoreId": "AoxXjM9NJT6P9C1MErkaawXaSchz8sFPYdQ9FyhmQz33",
-    "WebhookSecret": ""
+  "SilverPay": {
+    "BaseUrl": "http://31.97.57.205:8001",
+    "ApiKey": "sp_live_key_2025_production",
+    "WebhookSecret": "webhook_secret_2025",
+    "DefaultWebhookUrl": "https://littleshop.silverlabs.uk/api/silverpay/webhook",
+    "AllowUnsignedWebhooks": true
   },
   "RoyalMail": {
     "ClientId": "",