Add Grok media providers and improve selector routing

skills/creative/video-gen-prompting.md

@@ -14,6 +14,7 @@ For model-specific tips, see the linked guides below.
 |-------|-------|-------------|
 | **Sora 2 / Sora 2 Pro** | [OpenAI Sora 2 Cookbook](https://developers.openai.com/cookbook/examples/sora/sora2_prompting_guide) | Richest structured template. Advanced fields: lenses, filtration, grade, diegetic sound, wardrobe, finishing. |
 | **VEO 3.1 / VEO 3** | [Vertex AI Prompt Guide](https://cloud.google.com/vertex-ai/generative-ai/docs/video/video-gen-prompt-guide) | Best vocabulary reference tables. 14-component prompt structure. |
+| **Grok Imagine Video** | `creative/prompting/grok-prompting.md` | Best when prompts need reference-image placeholders like `<IMAGE_1>` and identity/product carryover. |
 | **LTX-2** | [LTX Prompting Guide](https://docs.ltx.video/api-documentation/prompting-guide) | 6-element structure. Audio/voice prompting. Strong "what to avoid" section. |
 | **HunyuanVideo 1.5** | [Tencent Prompt Handbook](https://github.com/Tencent-Hunyuan/HunyuanVideo-1.5/blob/main/assets/HunyuanVideo_1_5_Prompt_Handbook_EN.md) | Formula: Subject + Motion + Scene + [Shot] + [Camera] + [Lighting] + [Style] + [Atmosphere]. |
 | **Runway Gen-4** | [Runway Prompting Guide](https://help.runwayml.com/hc/en-us/articles/39789879462419-Gen-4-Video-Prompting-Guide) | "Focus on motion, not appearance." One scene per clip. Simplicity wins. |
@@ -175,6 +176,7 @@ Put dialogue in quotation marks: `Character says: "Hello world."`
 3. **If a shot misfires** — strip back. Freeze camera, simplify action, try again.
 4. **For consistency across clips** — repeat the same style/lighting/grade description.
 5. **Use seed values** — when you find a good result, save the seed for variations.
+6. **For Grok reference-image video** — assign each source image a clear role in the prompt using `<IMAGE_1>`, `<IMAGE_2>`, etc.
 
 ## Example: Generic Prompt Template