Switch Evotor integration to webhook-based token delivery flow

Replace OAuth 2.0 authorization code flow with Evotor's proprietary
webhook token delivery: POST /evotor/callback receives token server-to-server,
GET /evotor/link links it to the logged-in user's account.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/config.py

@@ -7,9 +7,8 @@ class Settings(BaseSettings):
     BASE_URL: str = "http://localhost:8080"
     PASSWORD_RESET_EXPIRE_MINUTES: int = 60
 
-    EVOTOR_CLIENT_ID: str = ""
-    EVOTOR_CLIENT_SECRET: str = ""
-    EVOTOR_SCOPES: str = "store:read product:read"
+    EVOTOR_APP_ID: str = ""
+    EVOTOR_WEBHOOK_SECRET: str = ""
 
     HEALTH_CHECK_INTERVAL_SECONDS: int = 600