feat(xai): add Grok Imagine video generation (/v1/videos) + CLI

Async video job proxy mirroring the existing image-generation layer split:
Next routes → src/sse/handlers/videoGeneration.js (auth gate, account
fallback loop, refresh persistence) → open-sse/handlers/videoCore.js
(transparent upstream proxy, 401 refresh-once/retry-once, secret sanitization).

- POST /v1/videos/{generations,edits,extensions}: byte-exact body forward
  (JSON + multipart), request_id passthrough, Idempotency-Key forwarded
- GET /v1/videos/{request_id}: status/progress/video.url passthrough
- Register grok-imagine-video (kind: "video"); add "video" to MODEL_TYPE_TO_KIND
  so video models stay out of chat lists (also fixes runwayml leak)
- 9router xai video CLI: submit → poll → atomic MP4 download
- No auto-retry of creation POSTs (billable jobs); rotate accounts only on
  401/403/429; sanitize Bearer tokens + credential values from errors/logs

Closes #1285

open-sse/providers/registry/xai.js

@@ -32,9 +32,13 @@ export default {
     { id: "grok-code-fast-1", name: "Grok Code Fast" },
     { id: "grok-3", name: "Grok 3" },
     { id: "grok-2-image-1212", name: "Grok 2 Image", params: ["n","response_format"], kind: "image" },
+    { id: "grok-imagine-video", name: "Grok Imagine Video", params: ["duration","aspect_ratio","resolution"], kind: "video" },
   ],
-  serviceKinds: ["llm","imageToText","webSearch","image"],
+  serviceKinds: ["llm","imageToText","webSearch","image","video"],
   imageConfig: { baseUrl: "https://api.x.ai/v1/images/generations", bodyFields: ["model","prompt","n","response_format"] },
+  // Async video jobs (POST returns { request_id }, GET polls until done/failed).
+  // Docs: https://docs.x.ai/developers/rest-api-reference/inference/videos
+  videoConfig: { baseUrl: "https://api.x.ai/v1/videos" },
   searchViaChat: {
     defaultModel: "grok-4.20-reasoning",
     endpoint: "https://api.x.ai/v1/responses",