Export the Reaction Model for Direct Access

[Silent-Watcher]

Improvement: Export Reaction Model from Plugin

Description:
Currently, the Reaction model is created internally. Provide a way to access it (e.g., schema.statics.ReactionModel) for advanced users who need to run complex queries or aggregations directly.

Acceptance Criteria:

• The Reaction model is attached to the schema's statics after plugin setup.
• It can be accessed via MyModel.ReactionModel.
• This is documented as an advanced feature.
• Does not affect the default plugin functionality.
• Add usage examples in docs