feat(channel): add customizable JS model-call scripts with split-panel editor

- Run user-authored async scripts per model with flat locals (prompt,
  images, messages, params, model, baseUrl, apiKey, http, request, poll,
  sleep, signal, onDelta); empty script falls back to system default.
- Wire image/video/audio/text request entrypoints through the plugin
  runtime, keeping default handlers unchanged.
- Split-panel script editor: variable/return docs on the left, CodeMirror
  JS editor on the right; title shows capability - model.
- Provide OpenAI and Gemini template buttons per capability; text template
  uses the /responses API; image template branches text2img vs img2img.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/package.json

@@ -14,6 +14,7 @@
     "dependencies": {
         "@ant-design/icons": "^6.1.1",
         "@ant-design/pro-components": "3.0.0-beta.3",
+        "@codemirror/lang-javascript": "^6.2.5",
         "@codemirror/lang-json": "^6.0.2",
         "@tanstack/react-query": "^5.100.9",
         "@uiw/react-codemirror": "^4.25.9",