- Add grok2 to PRESET_PROVIDERS with openai-compat gateway route
- Add grok-imagine-1.0 (image) and grok-imagine-1.0-video (video) preset models
- Extend OpenAIImageGenerateSize to support 1280x720 and 720x1280 resolutions
- Add grok2 to COMPATIBLE_PROVIDER_KEYS in router
- Add grok2 to VERIFIABLE_PROVIDER_KEYS for test-connection UI
- Show Base URL input and model tabs for grok2 provider
- Add i18n labels for Grok2 API compatibility layer badge
- Add GROK2_SETUP.md with configuration documentation