fix: add missing yeoman-generator dependency (#568)

* Initial plan

* fix: add missing yeoman-generator dependency to package.json

The CI workflow was failing because yeoman-generator is imported in
generators/app/index.js and other generator files, but was not listed
as a dependency in package.json. Adding it fixes the ERR_MODULE_NOT_FOUND
error that caused all 28 tests to fail.

Co-authored-by: rzhao271 <7199958+rzhao271@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: rzhao271 <7199958+rzhao271@users.noreply.github.com>

Author: Copilot