Statistics page: the statistics database's size, and a fullness bar on the disk tiles

The server section shows the statistics database's size (with its -wal and -shm) and how many answers the query log holds, linking to the dashboard's Storage panel; the disk tiles get the same bar as the dashboard. GET /stats/server has database {path, bytes, query_log_rows}.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -69,7 +69,8 @@ All notable changes to Jarl are documented here. The format follows
   the clients asking → everything one of them asks. `GET /stats/explore`.
 - **Storage** on the dashboard: the size of Jarl's databases (and how many
   answers the query log holds), and per disk Jarl uses a bar of how full it
-  is and how much of it the databases take.
+  is and how much of it the databases take. The Statistics page shows the
+  statistics database's size too, and its disk tiles get the same bar.
 
 ### Changed