feat: inject AI gateway model catalog into openclaw env

[Iamlovingit]

fix #68

Summary

• Inject the full AI Gateway model catalog into OpenClaw instance env while keeping auto as the default gateway alias.

Changes

• change CLAWMANAGER_LLM_MODEL from a single auto string to a JSON array like ["auto", ...active gateway models...]
• keep OPENAI_MODEL=auto for compatibility
• add backend tests for gateway model env injection
• update instance env descriptions in the UI to reflect runtime-injected model catalog

Routing Behavior

• sensitive-content governance is unchanged
• even if a user selects a specific non-auto model, requests with sensitive content may still be rerouted to an active secure model by AI Gateway
• if the selected model is already secure, it will continue to be used
• if risk rules require blocking or approval, those rules still take precedence

[Iamlovingit]

/lgtm