…erformance

- Separated the handling of JSON and HTML requests. The instance variable is not used in the HTML view, eliminating unnecessary data loading.
- Implemented JSON-specific requests to leverage the `start` and `end` parameters from the FullCalendar library. This restrict tags the fetched distributions to the specified dates instead of all historical records.
- Resolved the N+1 query issue by eager loading the associated partners with the distributions.
- Add an index on issued_at to speed up the filtering on distributions