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

cli/cli.js

@@ -67,6 +67,19 @@ const { ensureSqliteRuntime, buildEnvWithRuntime } = require("./hooks/sqliteRunt
 const { ensureTrayRuntime } = require("./hooks/trayRuntime");
 const args = process.argv.slice(2);
 
+// Subcommands (`9router xai video …`) run against an already-running gateway
+// and bypass the launcher flow (no runtime self-heal, no server spawn).
+if (args[0] === "xai" && args[1] === "video") {
+  const { run } = require("./src/cli/commands/xaiVideo");
+  run(args.slice(2))
+    .then((code) => process.exit(code))
+    .catch((err) => {
+      console.error(`❌ ${err?.message || err}`);
+      process.exit(1);
+    });
+  return;
+}
+
 // Self-heal SQLite runtime deps (sql.js + better-sqlite3) into ~/.9router/runtime
 // so the server can resolve them via NODE_PATH. Best-effort — sql.js is required,
 // better-sqlite3 is optional. Logs to stderr only on failure.
@@ -139,6 +152,11 @@ Options:
   --skip-update       Skip auto-update check
   -h, --help          Show this help message
   -v, --version       Show version
+
+Commands:
+  xai video --prompt "..." --output video.mp4
+                      Generate a Grok Imagine video via the running gateway
+                      (see: ${APP_NAME} xai video --help)
 `);
     process.exit(0);
   } else if (args[i] === "--version" || args[i] === "-v") {