refactor: reduce stats.ts duplication with factory pattern (F-10, F-21)

Introduce buildQuery helper and createListFetcher factory to eliminate
near-identical param building and list endpoint boilerplate. File reduced
from ~600 to ~310 lines (~48% reduction) with identical runtime behavior.

CHANGELOG.md

@@ -8,6 +8,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 
 ### Improved
 
+- **Cleaner internal API code.** The analytics data-fetching layer has been streamlined — 13 near-identical endpoint functions were consolidated using a shared pattern, cutting roughly half the code while keeping every feature working exactly as before. This makes it easier to add new analytics endpoints in the future and reduces the chance of inconsistencies between them.
+
 - **More reliable list rendering across the dashboard.** Pages, referrers, locations, devices, funnels, and other data lists now use stable identifiers (like page paths and referrer URLs) instead of array positions as their React keys. This prevents potential display glitches — such as stale data appearing in the wrong row — when lists are filtered, sorted, or updated in real time.
 - **Deleting a site now fully cleans up all its data.** Previously, deleting a site removed the site record but could leave behind orphaned analytics events in the database, slowly accumulating unused data. Now all events are cleaned up automatically in small batches before the site is removed, keeping your database tidy.