Without this import, SQLAlchemy's db.metadata doesn't know about the
installed_plugins table, so MigrationService.check_and_prepare's
db.create_all() never creates it on fresh installs. The plugin loader
then fails on cold start with "no such table: installed_plugins".
Pairs with the previous fix that moved the plugin loader to run after
the migration step. Both are required; this one is what Copilot's PR
review meant by "export the model from app/models/__init__.py".
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>