Add some convenience queries to equipment/equipment-category routes

Would be nice to query something like:
* `/api/equipment-categories/weapon?weapon_category=simple`
* `/api/equipment-categories/weapon?properties=finesse`

I'm sure there are others that folks would find useful.

Look at the existing equipment and equipment-category routes in the API, likely in a routes or controllers directory. Understand how query parameters are currently handled. The feature requires adding new query parameters like 'weapon_category' and 'properties' to filter results. Check the data model for equipment to see what fields are available. Test the new queries by running the API locally and verifying the filtered responses.

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