OpenCode provider gateway routing and timeout invariants

Route OpenCode providers explicitly through ${gatewayBase}/v1 using each provider's options.baseURL; do not rely on provider base-URL environment variables because resolveSDK() supplies a defined URL. Deep-merge options, avoid /v1/v1, and create an OpenAI entry when absent so routing still applies. For Lore-routed OpenAI and OpenAI Codex providers, set options.headerTimeout=false authoritatively: OpenCode has already merged its inherited 60-second timeout, while Lore owns the foreground deadline.