fix(openai): propagate environment context and sanitize antigravity generation config in interaction adapters

- Normalize conversation-context fields across OpenAI↔Interactions request/response translation by mapping both `previous_response_id`/`previous_interaction_id` and resolving `environment_id` (including nested `environment.id`) in both directions.
- Forward `agent_config` through translation and, for antigravity models, route output-token limits to `agent_config.max_total_tokens` while removing antigravity-incompatible `generation_config` knobs from emitted requests.
- Preserve `environment_id` through stream state so chat-completions and responses (stream/non-stream) outputs consistently carry it in final payloads.

Closes: #4995