chore(yabeda): Remove unused yabeda-mini manual test app

The app was never referenced by any spec or CI step and carried
maintenance weight (Gemfile.lock, SQLite DB, log files). The
sentry-yabeda adapter is already covered by unit and integration
specs in sentry-yabeda/spec/.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: dingsdax