Add user authentication and account management system

Features:
- User registration with username, email, password
- Login with JWT token authentication
- Password hashing with BCrypt
- Account settings & management
- Device linking to accounts
- Change password & password reset
- Account-User relationship (1-to-1 with game data)

Database entities:
- Account: User accounts with credentials
- DeviceAccount: Link devices to accounts (many-to-many)

API endpoints:
- POST /api/auth/register
- POST /api/auth/login
- POST /api/auth/change-password
- POST /api/auth/forgot-password
- POST /api/auth/reset-password
- GET /api/auth/me
- POST /api/auth/link-device
- DELETE /api/auth/unlink-device/{deviceId}

Starting resources for new accounts:
- 100,000 Gold
- 500,000 Cash
- Level 1

Ready for VPS deployment with HTTPS.

RR3CommunityServer/appsettings.json

@@ -6,6 +6,12 @@
     }
   },
   "AllowedHosts": "*",
+  "Jwt": {
+    "Secret": "RR3CommunityServer_SecureJwtSecret_ChangeThisInProduction_MinimumLength32Characters",
+    "Issuer": "RR3CommunityServer",
+    "Audience": "RR3Community",
+    "ExpiryDays": 30
+  },
   "AssetsBasePath": "Assets/downloaded",
   "CustomAssetsPath": "Assets/custom",
   "ModsPath": "Assets/mods",