feat: add strict Node.js version compatibility checks

[ethenotethan]

Running ecloud app deploy with an older node version would fail with insufficient user context:

ECLOUD_ENV=sepolia-dev ecloud compute app deploy --instance-type g1-standard-4t
✔ Build from verifiable source? No

Found Dockerfile in /Users/ethen/sovereign-research-agent
✔ Choose deployment method: Build and deploy from Dockerfile

📦 Build & Push Configuration
Your Docker image will be built and pushed to a registry
so that Ecloud CLI can pull and run it in the TEE.

Detected authenticated registries:
  dockerhub: ethenotethan/sovereign-research-agent:latest
  dockerhub: ethenotethan/sovereign-research-agent:latest
  dockerhub: ethenotethan/sovereign-research-agent:latest

✔ Select image destination: ethenotethan/sovereign-research-agent:latest

App name selection:
✔ Enter app name: sovereign-research-agent
Failed to fetch instance types: Environment sepolia is not available in this build type. Available environments: sepolia-dev
✔ Do you want to view your app's logs? Yes, publicly viewable by anyone
✔ Show resource usage (CPU/memory) for your app? No, disable resource usage 
monitoring
    ReferenceError: crypto is not defined

Changes

• Add preflight Node.js version validation (>=18) in CLI entry points (bin/run.js, bin/dev.js) before loading dependencies
• Declare engines field in both cli and sdk package.json files.