Add private model relay provider and register internal relay models

[hifizz]

Motivation

• Add support for an internal "private-relay" model gateway to let the app route requests to private/self-hosted OpenAI-compatible model relays.
• Keep these private-relay models out of public surfaces and billing by marking them as internal previews.
• Provide configuration helpers and clear errors when the private relay is not configured.

Description

• Add PRIVATE_RELAY_BASE_URL and PRIVATE_RELAY_API_KEY to .env.example for configuring the private relay endpoint and key.
• Extend ChatModelProvider with private-relay and register three internal models (private-relay-gpt-5.6-luna, private-relay-gpt-5.6-terra, private-relay-gpt-5.6-sol) in the model registry with unbilledPreview: true and no public surfaces.
• Introduce lib/ai/private-relay.ts that provides normalizePrivateRelayBaseURL, isPrivateRelayConfigured, and privateRelayChatModel using createOpenAICompatible to create an OpenAI-compatible provider for the relay.
• Update lib/ai/provider.ts to import and route private-relay models, include them in isModelConfigured checks, and exclude them from the generic PROVIDER_ENV mapping so they use the dedicated relay logic.

Testing

• Ran TypeScript build and type-check with pnpm -w build and no type errors.
• Ran the existing test suite with pnpm -w test and lint with pnpm -w lint, both completed successfully.

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Project	Deployment	Actions	Updated (UTC)
thread-chatbot	Error		Aug 30, 2026 8:00am

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