When switching providers via 'hermes model', the previous provider's
api_mode persisted in config.yaml. Switching from Copilot
(codex_responses) to a chat_completions provider like Z.AI would send
requests to the wrong endpoint (404).
Set api_mode = chat_completions in the 4 provider flows that were
missing it: OpenRouter, custom endpoint, Kimi, and api_key_provider.
Co-authored-by: Nour Eddine Hamaidi <HenkDz@users.noreply.github.com>