Add date filter clearing and small changes to README

[CalamityC]

No description provided.

[MyPyDavid]

Ive added some things, css tweaks and added a filter for catalog in the "Project progress" chart.

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Extends the statistics dashboard filtering and improves its frontend infrastructure. Date filters can now be cleared individually and are applied to catalog usage and project-progress statistics as well as the time charts. Project progress can additionally be filtered by catalog, using a new site-scoped statistics API. Exports and data tables follow the active filters, asynchronous updates handle stale/error responses safely, and the changes are covered by new JavaScript and Django tests. The PR also hardens the GitHub Actions workflow and updates documentation and translations.