feat(cli): add remove-background command for transparent video

Adds `hyperframes remove-background` — a local-AI subcommand that mattes a
video or image with the u2net_human_seg ONNX model and emits a transparent
WebM (VP9-alpha), ProRes 4444 .mov, or RGBA PNG. Drops directly into any
composition's <video> tag — no green screen, no API keys, no upload.

Auto-picks the fastest available execution provider via onnxruntime-node:
CoreML on Apple Silicon, CUDA when HYPERFRAMES_CUDA=1, CPU otherwise.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/cli/package.json

@@ -33,10 +33,12 @@
     "giget": "^3.2.0",
     "hono": "^4.0.0",
     "mime-types": "^3.0.2",
+    "onnxruntime-node": "^1.20.0",
     "open": "^10.0.0",
     "postcss": "^8.5.8",
     "prettier": "^3.8.1",
-    "puppeteer-core": "^24.39.1"
+    "puppeteer-core": "^24.39.1",
+    "sharp": "^0.34.0"
   },
   "devDependencies": {
     "@clack/prompts": "^1.1.0",