chore(browser): extract network interceptor script

[jackwener]

Summary

• move the injected fetch/XHR network interceptor out of src/cli.ts and into src/browser/network-interceptor.ts
• keep browser command registration focused on command wiring while preserving the existing injected script verbatim

Verification

• npm run typecheck
• env HOME=/tmp/opencli-cli-test-home USERPROFILE=/tmp/opencli-cli-test-home npm test -- --run src/cli.test.ts
• npm run build