Patch Changes 8edc775: feat (provider/xai): support Grok Imagine Video 1.5. Adds the `grok-imagine-video-1.5` model id and native `1080p` for text-to-video and image-to-video (the standard `resolution: '1920x1080'` now maps to `1080p`). Reference-to-video remains capped at `720p`, so a `1080p` request in that mode is downgraded with a warning. Also fixes reference routing: previously any non-empty `inputReferences` array selected reference-to-video, so an array holding only a non-image reference sent `reference_images: []` with no usable references.

3d05053: feat (provider/xai): add `referenceVoiceIds` for reference-to-video reference audio. Pass up to 3 xAI preset voice ids (e.g. `['eve']`) and reference them from the prompt with ``–``; they are sent as `reference_audios: [{ voice_id }]` on `POST /v1/videos/generations`.