Fix API build: disable isolated-vm sandbox temporarily

- Remove isolated-vm dependency (requires native compilation)
- Stub out sandbox to return graceful error
- Extension handlers will fail with 'sandbox unavailable' until isolated-vm is configured

This allows the API to build and run without native compilation.

Author: eldinmiller

api/package.json

@@ -18,7 +18,6 @@
     "@supabase/supabase-js": "^2.39.0",
     "fastify": "^5.2.1",
     "fastify-plugin": "^5.1.0",
-    "isolated-vm": "^4.7.2",
     "pino-pretty": "^13.0.0",
     "zod": "^3.23.8"
   },