feat(cli): optimize startup time

[codeaholicguy]

Summary

Optimize ai-devkit CLI startup by replacing eager command registration with a lightweight runtime and lazy command loading.

Changes

• Add a startup benchmark script and CI gate for CLI startup/help paths.
• Keep --version inline in cli.ts so it avoids loading runtime code.
• Add cli-command-manifest.ts as the lightweight source of truth for top-level command metadata.
• Add cli-runtime.ts for static root/top-level help rendering and lazy command execution.
• Lazy-load Commander and only the selected command module for real command execution.

Verification

• npm run build
• npm test -w packages/cli
• npm run test:e2e
• npm run benchmark:startup -w packages/cli