fix: make Odoo login configurable via ODOO_USER (default __system__)

Some Odoo instances require the user's actual login/email for API key
auth rather than the __system__ special login. ODOO_USER defaults to
__system__ for standard Odoo 16+ installs.

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

agent_service/config.py

@@ -8,6 +8,7 @@ class Settings(BaseSettings):
     # Odoo
     odoo_url: str = 'http://localhost:8069'
     odoo_db: str = 'odoo'
+    odoo_user: str = '__system__'
     odoo_api_key: str = ''
 
     # Ollama