Add Cloud Agent development environment config

[JeremySNR]

Summary

Sets up a Cloud Agent development environment for ClipForge by adding a repository-managed .cursor/environment.json. Because ClipForge is a single Electron + Vite + React + TypeScript desktop app with no backend/database/container, the setup is intentionally minimal: the Cursor default base image already provides Xvfb and every Electron system library, so the only bootstrap step is an idempotent dependency install.

{
  "name": "ClipForge",
  "install": "npm ci"
}

• No build (Dockerfile/image): the default image already has xvfb-run, libnss3, libgtk-3, libgbm, libasound, libatk, libcups, libdrm, and the rest of Electron's runtime libraries.
• No start/terminals: this is a desktop app, not a long-running server. The GUI is launched on demand under Xvfb (see AGENTS.md / scripts/smoke-test.sh).
• install uses npm ci against the committed package-lock.json so bundled ffmpeg-static, ffprobe-static, and the onnxruntime-node native binary are restored deterministically.

Validation (on this VM)

Check	Result
npm ci	Succeeded (411 modules; electron, ffmpeg-static, ffprobe-static, onnxruntime-node native all present)
npm ci idempotence	Passed twice
npm test (vitest)	228 passed / 29 files
npm run typecheck	Passed (node + web tsconfigs)
npm run lint (eslint)	Passed
scripts/test-pipeline.ts (offline ffmpeg render)	Passed (probe, audio, thumbnails, caption layout, 12 ASS styles, 7 render variants, auto-frame)
scripts/smoke-test.sh (GUI under Xvfb)	Passed — built, seeded demo, launched Electron, ran "caption whole video" for real, captured all 7 screens

The smoke test is a real end-to-end GUI run: the clips screen shows AI-scored clips and the editor shows a live vertical preview with burned-in karaoke captions, trim, layout and auto-zoom controls.