fix(stats): refresh Overview data after deleting sessions

- Add a refresh key to OverviewTab that refetches overview, streak calendar, and known-words summary after single, day, or anime session deletes
- Reset loading/error state in useStreakCalendar on refetch
- Add OverviewTab tests covering each delete mode and a failed delete
- Document the automatic refresh and add changelog fragments

docs-site/immersion-tracking.md

@@ -42,6 +42,8 @@ To share stats and watch history between machines, use [`subminer sync <host>`](
 
 Recent sessions, a streak calendar, watch-time history, and totals for completed episodes and shows.
 
+Deleting a session or session group refreshes the Overview totals, charts, calendar, and vocabulary summary automatically.
+
 ![Stats Overview](/screenshots/stats-overview.png)
 
 ### Library